John-117

"They let me pick. Did I ever tell you that? Choose whichever Spartan I wanted. You know me. I did my research. Watched as you became the soldier we needed you to be. Like the others, you were strong and swift and brave. A natural leader. But you had something they didn't. Something no one saw, but me. Can you guess...? Luck."

- Cortana

Master Chief Petty Officer of the Navy John-117 is a SPARTAN-II commando of the UNSC Naval Special Warfare Command. He served as one of the most important figures of the Human-Covenant War. With nearly 30 years of active duty, he is one of the most decorated war veterans in the United Nations Space Command and has earned every known medal in the UNSC except the Prisoner of War Medallion. In 2553, John-117 went missing in action after the Battle of Installation 00, when he and the current Arbiter Thel 'Vadam stopped the Flood threat.

He is the protagonist and main playable character in Halo: Combat Evolved, Halo 2, and Halo 3. In the games, John is only ever referred to by name once, by Cortana, in the ending cutscene of Halo 3 before the credits. He is referred to universally by humans simply as the "Master Chief", "Chief" for short and "Sierra-117". The Covenant is aware of the power of the Spartans, and refer to the Master Chief as "the Demon". John is referred to as "Reclaimer" by both 343 Guilty Spark and 2401 Penitent Tangent, although this seems to be a universal title given to all humans, rather than specifically referring to John-117.

Childhood and Spartan training
Born in about 2511, John lived with his mother and father in Elysium City, on the colony world of Eridanus II. He attended the Elysium City Primary Education Facility Number 119. As a child, John had brown hair, freckles, and a small gap between his front teeth. In a memory, John recalled that his mother was "kind and smelled of soap." The would-be UNSC Marine Lieutenant Parisa was a childhood friend of John's. John once saved her from drowning at Lake Gusev, after which John promised to marry her and keep her safe. A photo of the two was also taken by Parisa's father soon after, and would be kept as a memory by Parisa long after she thought John had passed away.

At the age of six, he was identified by Dr. Catherine Halsey as one of 150 preliminary candidates for the SPARTAN-II Program. John was an ideal physical and mental candidate, standing a head taller than the majority of his schoolmates, having greater physical proportions, possessing greater strength, exhibiting superior reflexes, and having an aggressive drive for success. When Dr. Halsey and Lieutenant Jacob Keyes visited Eridanus II in 2517 to study him, they were impressed with his intellect and luck. In a final test of his viability as a candidate, he was asked to determine which side an old coin would land on. He watched the coin as it flew in the air and caught it before it could land; correctly stating which side was face-up, on the side of the eagle. Later that same year, John and 74 other six-year-old children were "conscripted": they were covertly kidnapped from their homes and replaced with flash clones, all of which would later die of natural causes to cover up the kidnappings. John, along with the other candidates, was taken to the planet of Reach. Dr. Halsey informed them of the SPARTAN-II Program and how they would be the protectors of Earth and all its colonies. The next morning John discovered his service tag, stitched into his training uniform, and his new name: John-117. .

John began a new life, training with other Spartans under Chief Petty Officer Franklin Mendez. For eight years he learned history, military strategy, weapons, and was given physical fitness training. Early on, he bonded with Kelly and Sam, who would become two of the few close friends he would ever have.

During his training, John quickly proved himself to be considered one of the program's top candidates. Both Dr. Halsey and Chief Mendez identified him as one of four emerging leaders within the Spartan-II group, along with Kurt-051, Jerome-092, and Frederic-104. Dr. Halsey expressed her belief the most strongly in John as having the skills and natural ability to lead the entire Spartan-II group, although Mendez disagreed, instead believing Kurt would fulfill that role.

When the Spartans were eight years old, they were sent on a training mission in which they were dropped over a forest located deep in one of Reach's snow-capped mountain ranges and expected to get safely to their extraction Pelican dropship. The children also had instructions to leave the last child arriving behind, or the punishment would be painful, but John-117 knew that he could not do that. After telling the Spartans where to meet, the Spartans looked to him as their leader, a role he was initially surprised to be given, but eventually accepted. When the group came upon the Pelican, it was guarded by armed men. Those men were actually UNSC Marines, but were not in uniform, thus leading the Spartans to mistake for a hostile threat. John showed early acumen in critical thinking and tactics, not wishing to take for granted that guards would be friendly toward them. He came up with a plan to take the men down, capture the dropship, and ensure the safe extraction of every team member, as he made sure he was the last person aboard. To do this he ended up hijacking the dropship with the help of Déjà, and beat down the men with stones, causing severe injuries among the Marines. Chief Mendez was not visibly pleased, as John had attacked his Marines and no one had been left behind. But both Mendez and Halsey recognized John's initiative, and promoted him to squad leader. After this, despite other Spartans rising in rank and at least a couple rising to lead their own teams, he remained the de facto leader of the Spartans as a whole.

John's leadership skills were correctly observed, as the result from their mission clearly solidified his role as the overall leader of the Spartan-IIs. He also became the established leader of the Spartan-II's Blue Team.

At the age of 14, John underwent the dangerous SPARTAN-II Augmentation Procedures. These procedures caused 30 of the Spartan trainees to die, and 12 to become physically disabled. John was one of 33 Spartans who made it through the process unscathed, while the rest who could still operate were sent for jobs in the Office of Naval Intelligence. At only 14 years old, it is said that John had a body of an 18-year old Olympic athlete; the augmentation process gave the Spartans faster reflexes, greater strength, enhanced eyesight, and made their bones nearly unbreakable. Following their augmentation procedures, John and the other Spartans were transferred to the Atlas in order to recover in a microgravity environment. During his first visit to the Atlas' gym, John was confronted by four ODSTs, whose sergeant then ordered the five of them into the boxing ring. In the ensuing fight, John killed two of the ODSTs, and left the others severely injured. According to Major Antonio Silva, this incident was orchestrated by the Office of Naval Intelligence in order to test the Spartans' augmentations.

Early military career
John-117's first mission was against rebels in the asteroid belt of the Eridanus System, where his home world was located. He was shot in the side by live ammunition while leading his squad to capture rebel leader Colonel Robert Watts, without heavily injuring him. The mission caualty list is 11 dead rebel soldiers and un-known rebel civilians. He received a Purple Heart after this mission for taking a round in the side.

Three months after the Eridanus mission, John and his Spartans were briefed on the massacre that took place on Harvest shortly after first contact with the Covenant. A short time later, the, under the command of Captain Wallace, brought the Spartans and Dr. Halsey to the Damascus Testing Facility at Chi Ceti, where they received the MJOLNIR Mark IV Powered Assault Armor. When a Covenant ship, the Unrelenting, attacked the Commonwealth, John and the SPARTAN-IIs took part in their first battle with the Covenant. The Spartans used thrusters to launch from a Pelican dropship. Each Spartan carried an ANVIL-II Air-to-Surface Missile to destroy the Covenant ship. Only two other Spartans made it to the ship with John: Samuel-034 and Kelly-087. They entered the ship through a hole in its hull, caused by a MAC round from the Commonwealth. They succeeded in completing the mission and destroyed the Covenant ship, but due to a breach in Sam's armor, caused by retaliation fire from Covenant forces, he was unable to leave the Covenant ship. Volunteering to stay behind and ensure the destruction of the enemy vessel, Sam was killed in the ensuing explosion. John was affected profoundly at the loss of one of his friends. This UNSC victory against the Covenant showed John that the Covenant weren't invincible and could be beaten, but at a very high cost. John and the remaining Spartans would fight the Covenant for the next 27 years, employing their MJOLNIR armor.

In 2544, John, along with Fred-104, Kelly-087, Solomon-069 and Arthur-079, was part of a mission to rescue Dr. Catherine Halsey from a Covenant fleet. The team utilized OF92/EVA "Booster Frame" fighters, which were designed for ship boarding actions, and infiltrated a Covenant Assault Carrier. Aboard the Assault Carrier, John encountered Major Domo Thel 'Lodamee, who challenged John to an Energy Sword duel. Thel was forced out of the duel when his Fleetmaster separated the lower section of the Assault Carrier to kill the Spartan, pulling him back into the upper section. Both combatants were left unscathed. The Spartans completed the mission and rescued Dr. Halsey, but Arthur and Solomon were killed. John was saddened by his teammates' deaths and vowed to be stronger and never let such a loss happen again.

John served in over 200 missions against the Covenant, including the Harvest Campaign, the Battle of Jericho VII, where he and a handful of Spartans single-handedly killed over a thousand Grunts, and the Battle of Sigma Octanus IV, in which John and his Blue Team detonated a HAVOK Nuclear Warhead to clear Covenant forces from the city of Côte d'Azur. This was one of only a few UNSC victories against the Covenant. By summer of 2552, he had received every medal awarded by the UNSC except the Prisoner of War Medallion the reason being the Covenant forces do not take prisoners and John would not allow himself or any other SPARTAN to be captured by the enemy.

Fall of Reach
The Fall of Reach, though brief, was of great significance for John. Here he received the MJOLNIR Mark V Powered Assault Armor, which improved his strength and reaction time more effectively than his older Mark IV suit. He was also introduced to and partnered with the AI Cortana, who would become a close friend and ally to him. In the first test of their partnership, the two were put through a practically suicidal test in an attempt by Colonel Ackerson to get rid of John. John refused to cheat the test and was determined to win it by Ackerson's rules. Despite nearly being killed, Cortana and John's teamwork had them pass the test in an early show of the incredible partnership the two would come to develop. The majority of the Spartans went to the planet's surface to protect the Orbital Defense Generators which powered the planet's twenty Orbital Defense Platforms. John, with Linda and James, was sent to Reach Station Gamma to destroy an unsecured NAV database onboard the. If the Covenant obtained the database, they would discover the location of every human world, including Earth; the location of Earth by then was still a closely guarded secret. The NAV database was destroyed, but Linda and James were ambushed by Covenant Sangheili; James was lost in space, and Linda was critically wounded. John saved four other Marines on the station, including Staff Sergeant Avery Johnson. The team returned to the  and was placed into cryo-sleep as the ship landed on, then fled Reach and, following the Cole Protocol, jumped into Slipspace with coordinates deduced by Cortana from constellation data retrieved earlier, in hopes of leading the Covenant away from Earth.

Installation 04
Once the ship had arrived safely at Installation 04, it emerged that the UNSC Halcyon-class cruiser  had been followed through Slipspace by around a dozen Covenant ships, who ultimately engaged the Autumn and sent several boarding parties to board the ship. Captain Jacob Keyes ordered John to be woken from cryosleep, and tasked him with ensuring the escape of, Cortana (who was acting as the ship's AI), while he crash-landed the Pillar of Autumn on the unidentified ring.

Initially, fighting on Halo was between UNSC and Covenant forces, but after Captain Keyes unwittingly releasing an ancient parasite, the majority of both forces were infected, and the fighting shifted to combating the new enemy.

Flood infestation of Installation 04
"Do you have any idea what that bastard almost made you do?"

- Cortana

"Yes... activate Halo's defenses, and destroy the Flood, which is why we brought the Index to the Control Center."

- John-117

John-117 was sent out by the Installation's Monitor, 343 Guilty Spark, to retrieve the Index, an activation device for the Halo ring that the Master Chief is led to believe would destroy all Flood forms within a large radius. Upon John's return to Halo's Control Room, Cortana revealed that Halo's true purpose is to destroy all sentient life forms in the galaxy to starve the Flood, not to kill the Flood themselves. John was then forced to disrupt Halo's firing system by disabling Halo's Phase Pulse Generator in order to delay the Monitor's plan.

John soon joined the three-sided combat among the Covenant, the Flood and the Forerunners' Sentinels. Soon after, he tried to rescue Captain Keyes, but was too late. Captain Keyes had been transformed into a Proto-Gravemind Flood form. After infiltrating the Truth and Reconciliation, the Chief managed to retrieve the Captain's neural implants, which he used to activate the Pillar of Autumn's self-destruct sequence. After the sequence was aborted by 343 Guilty Spark, he proceeds to manually overload the fusion reactors, which would subsequently destroy both the Pillar of Autumn and Installation 04.

After successfully destroying the fusion reactors on the Pillar of Autumn, John-117 used a Warthog to reach the extraction point where Pelican Echo 419 would pick him up. John-117 reached the extraction point, only to witness the Pelican crashing into the Autumn's hull after being shot down by a pair of Banshees. The Chief quickly diverts his escape route towards the ship's hangar bay, which housed a Longsword fighter. Only a handful of UNSC forces survived, including Lieutenant Elias Haverson, Corporal Locklear, Warrant Officer Sheila Polaski, then-Staff Sergeant Avery Johnson, Private First Class Chips Dubbo, and then-Staff Sergeant Pete Stacker.

Journey to Earth and Operation: FIRST STRIKE
After the destruction of Alpha Halo, Cortana and the Master Chief fled through space in the Longsword they had escaped in. He discovered three cryotubes floating nearby, one containing Linda-058, and retrieved them. Soon after, the Covenant flagship Ascendant Justice came into the system along with a few cruisers, some of which had possibly escaped Halo's destruction and called the flagship to Threshold. A nearby Pelican dropship which had docked on an asteroid floating among Halo's debris field,fired at the cruiser to distract it. After a successful escape from the Covenant battle group, John linked the two vessels and brought its passengers aboard the Longsword. The crew of the Pelican then helped John in capturing the Ascendant Justice; the human survivors then traveled to Reach to look for surviving Spartans. John eventually located some of his fellow SPARTAN-IIs on Reach, along with Vice Admiral Danforth Whitcomb and Dr. Catherine Halsey. They returned to the ship and linked it with the UNSC Frigate Gettysburg. They began to travel toward Earth and soon discovered a base belonging to the Eridanus Rebels, led by Governor Jacob Jiles. After receiving some repairs, they were forced to abandon the rebels in the face of a Covenant assault, and made their way toward the Covenant refit-and-repair station, Unyielding Hierophant, where an enormous fleet was poised to invade Earth.

John faced a dilemma regarding the combat data on the Flood which Dr. Halsey had given him. Providing the standard data set to Lieutenant Haverson would protect Sergeant Johnson from possible experimentation by ONI. However, providing him the complete data, which contained reference to Sergeant Johnson's escape from the Flood due to his Boren's Syndrome, would result in Johnson's death.

John and the few remaining SPARTAN-IIs, Linda-058, Grace-093, William-043, and Fred-104, focused on finding a way to stop the Covenant from reaching Earth, the location of which had been discovered. They decided to destroy the 'Unyielding Hierophant. The SPARTAN-IIs infiltrated the station; after spending eleven hours on board, they arrived at a temple, where a copy of Cortana warned them of the Brute guards stationed at the temple. Linda took a sniping position and the other four Spartans entered the temple. They were ambushed by Brutes, and John was nearly killed, but the team managed to kill their attackers. Grace, however, was killed by three Brute Shot rounds. John activated the fail-safe on her armor, denying her compromise by the Covenant.

The team sabotaged the generators in the Unyielding Hierophant; as they escaped through a side door, the fail-safe on Grace's armor activated, disintegrating a Covenant lance. John, Fred, and Will were quickly spotted by three Banshees, but their Elite pilots were killed by Linda's sniper fire. The Banshees were then captured by the Spartans. John doubled back to retrieve Linda, who killed four more Banshee pilots who were attempting to kill John. They then escaped by destroying a glass atrium, and arrived back at the Gettysburg.

Vice Admiral Whitcomb and Lieutenant Haverson piloted the Ascendant Justice straight toward the Unyielding Hierophant. Whitcomb discussed the battles of the Alamo and Thermopylae with John, then prepared to fight the Covenant off while the Unyielding Hierophant's fusion reactor detonated. Each of the 500 Covenant ships maneuvered next to the Ascendant Justice. The Admiral and the Lieutenant were killed when the fusion reactor exploded, annihilating 486 ships of the Covenant fleet, leaving only around a dozen intact; these ships later joined the Prophet of Truth's rebuilt fleet in the attack on Earth. John left after witnessing Whitcomb's and Haverson's sacrifice, and arrived at Earth with the last members of his team, Linda, Will, and Fred, as well as Johnson and Cortana.

Battle of Earth
"Sir, permission to leave the station?"

- John-117

"For what purpose Master Chief?"

- Terrence Hood

"To give the Covenant back their bomb."

- John-117

Aboard Cairo Station, John received the MJOLNIR Mark VI Powered Assault Armor and attended an awards ceremony with the newly-promoted Lieutenant Commander Miranda Keyes and Sergeant Major Johnson. The ceremony was interrupted by the arrival of Regret's Fleet, initiating the Battle of Earth. John successfully repulsed Covenant boarders from the station. Upon discovering a Covenant Anti-Matter Charge on board Cairo Station, John fought his way through waves of Elites, Grunts, and Drones until he reached the bomb and allowed Cortana to access and deactivate it by transfering her back to his suit. Afterwards, she chose to rejoin him despite his offer for her to remain on the station. He used the charge against the Covenant by launching himself and the device, via decompression of one of the station's launch bays, towards an Assault Carrier. A timely strike by Longsword interceptors opened a breach in the warship's hull, allowing John to direct the bomb into the ship's fusion core. He then proceeded to use the blast from the bomb to launch himself back into the.

John was then deployed to New Mombasa, East African Protectorate aboard the, in an attempt to board Regret's Carrier. Both of the strike teams' Pelican dropships were shot down by a Scarab. John and the surviving Marines on his team fought their way to the other Pelican's crash site. After rendezvousing with Gunnery Sergeant Pete Stacker at Hotel Zanzibar in Old Mombasa, the Master Chief destroyed Covenant units along the shore of the city as he chased the Scarab. Upon arriving at the edge of Old Mombasa, John received a Scorpion Tank from Sergeant Major Johnson.

After fighting through numerous highway tunnels and suburbs, John reached the city center, where Marines under the command of Staff Sergeant Marcus Banks were pinned down by Covenant forces. With the assistance of the Marines and a large stockpile of weapons, John boarded the Scarab and was able to destroy it and the Covenant forces protecting it. John was then transported to In Amber Clad to intercept the Prophet of Regret's flagship. When the flagship started to enter Slipspace, Lieutenant Commander Keyes was granted permission to follow it. John and all on board In Amber Clad were brought to Installation 05.

Installation 05
Forced to act quickly once at Installation 05, John deployed groundside in an SOEIV along with several Orbital Drop Shock Troopers. This team was tasked with locating and assassinating the Prophet of Regret. Cortana informed John of Regret's intent to fire Halo as soon as possible. He tracked the Prophet of Regret to a temple in the middle of a lake, but not before witnessing hundreds of Covenant vessels coming out of Slipspace, followed by High Charity. He quickly dispatched the Prophet of Regret, and escaped the temple shortly before it was destroyed by an overhead cruiser. John jumped off the edge of the structure and into the lake below.

Losing consciousness and being unable to swim in the lake, he was captured by the Flood's central intelligence, the Gravemind. Shortly after, the Arbiter was also captured. The Gravemind appealed to the common interest of the Flood and the humans share, that of not wishing the Halos to be fired. John agreed. The Gravemind then tasked both captives with locating the Index, sending them to the two most likely locations. John was sent to High Charity, interrupting a sermon by the Prophet of Truth. The conflict between the Sangheili and Jiralhanae was beginning, leading the Covenant on the path to civil war: John was caught right in the middle.

John chased the surviving Hierarchs through High Charity, eventually catching up to the Prophets and their Brute escorts. However, only a dying Prophet of Mercy, who had been compromised by a Flood Infection Form, was left to tell him that Truth was heading to Earth. John faced another crucial dilemma: the Covenant had the Index and could activate Halo; however, Earth's stood little chance of withstanding Truth's reassembled fleet. Ultimately, John followed the latter priority, forced to leave Cortana behind so that if Halo were activated, she would detonate In Amber Clad's reactors, not wanting to risk detonating them remotely. John boarded the Forerunner Dreadnought, which was bounding for Earth, but not before promising to return for Cortana after he stopped Truth.

Return to Earth
"Master Chief, you mind telling me what you're doing on that ship?"

- Lord Hood

"Sir, finishing this fight."

- John-117

After a series of firefights, captures and escapes, John exited the Dreadnought and crash-landed on Earth, where he was found by Sergeant Johnson, the Arbiter, and the rest of their squad. Johnson believed the Chief to be dead, and requested heavy lifting gear in order to recover the Spartan's body. However, John awoke to battle-ready condition only moments later, showing his incredible tolerance to pain and shock. He attempted to attack the Arbiter, believing that the Elites were still the enemy. Johnson informed him that the two races were now allies, as the disillusioned Arbiter and the Sangheili had defected from the Covenant.

John and the Marines traveled through the jungle, searching for evacuation to a nearby military base. Johnson and his team split up from John and the Arbiter; the sergeant and his squad were soon captured by loyalist Covenant Brutes, although they were rescued by John and 'Vadam. After taking heavy fire from Phantoms, a Pelican dropship evacuated the team to a UNSC base known as Crow's Nest.

The base soon came under attack, but not before Fleet Admiral Terrence Hood told John his plan. Lieutenant Commander Keyes decided to evacuate all forces, many of whom were injured. John, Thel and the remaining UNSC Marines defended the base during its evacuation, planting a massive bomb to destroy the base along with the invading Covenant forces. The Master Chief fought his way through many Brutes, escaping the explosion in an elevator. He met up with several Marine survivors underground, and they escaped the base and headed for the city of Voi along Tsavo Highway, crushing Covenant resistance on their way.

At the Battle of Voi, John pushed through many Loyalist forces as he made his way to what was believed to be the Ark. Rather, this turned out to be a device that opened up a portal to the Ark. With Marine support, John destroyed three Anti-Air Wraiths, a Scarab, and a Covenant Anti-Aircraft Battery, allowing Lord Hood's remaining frigates to fire upon Truth's Dreadnought, with little effect. Truth then activated and fled through the Portal with his remaining Loyalist forces, while the UNSC remained behind to determine their next move.

Just as the battle seemed finished, a Flood-infested Covenant warship crash-landed in Voi. John, 'Vadam, and the remaining Marines fought to contain the Flood infection, learning that the only way to contain the Flood was to destroy the warship. During the battle, Shipmaster Rtas 'Vadum came to aid the UNSC. He deployed a Special Operations Sangheili strike team through Orbital Insertion Pods, assisting John as he was sent to retrieve Cortana from the cruiser, as it was believed that she was on board. Aided by 343 Guilty Spark, John retrieved a damaged data device and was brought aboard 'Vadum's flagship, Shadow of Intent. This data turned out to be only a message, rather than Cortana herself. The Sangheili were able to stop the Flood infestation by glassing the city and its surroundings, much to Hood's displeasure.

The Sangheili and the UNSC watched Cortana's recording, which contained a warning that High Charity, now overwhelmed and controlled by the Gravemind, was heading for Earth. However, she offered hope, with information of a way to stop the Halos from firing and neutralize the Flood threat. Convinced of the reliability of Cortana's message, John resolved to journey to the Ark, while Hood mobilized remaining UNSC forces on Earth. John accompanied a joint UNSC-Sangheili task force through the portal aboard the to the Ark.

Installation 00
The Sangheili carried UNSC forces through the Slipspace portal which led to the Ark. The team was determined to stop Truth from activating the remaining six Halos. They descended in Pelicans while the Shipmaster's fleet fought hard against the Brute ships. They flew to the surface of the Ark to eliminate the Covenant Loyalists in the area, to secure a landing zone for Forward Unto Dawn, and to find the Ark's Cartographer. Traveling in Scorpions, Warthogs, and captured Prowlers, John and other Marines located the Cartographer and learned that Truth was in the Installation's Citadel. John then escaped from the Cartographer and proceeded to assault the fortress.

John-117, Thel 'Vadam, and a squad of Marines were assigned to separately attack three Barrier Towers, which were emitting a protective shield around the Citadel. Although John and 'Vadam managed to deactivate two towers, Sergeant Johnson was captured in the battle, being spared to serve as a Reclaimer. John, 'Vadam, and the Elites deactivated the last tower, lowering the shield. Just as the Shadow of Intent was about to destroy the Citadel, the Flood-controlled High Charity exited Slipspace, bringing the Flood into the battle and disabling the Shadow of Intent.

After defeating the last remnants of the Loyalist forces around the Citadel, including two Scarabs, John and 'Vadam entered the Citadel. Although Miranda Keyes had forced her way in, breaking through the central window with her Pelican, she was soon surrounded. As she hesitated before killing Johnson and herself, Truth shot and killed Keyes with a Spiker. Truth then forced Johnson to begin the activation sequence. In an unexpected turn of events, John and 'Vadam made a temporary alliance with the Flood to stop the activation of the Halos. The final Loyalist defenses were crushed by the Flood as John and the Arbiter reached Truth, who was already being infected by the Flood. Then 'Vadam executed him with his energy sword, while John deactivated the rings.

The Gravemind then betrayed John and 'Vadam, laughing as it had succeeded in preventing its own destruction. After fighting past waves of Flood, the two escaped. As they were leaving the Citadel, John saw a vision of Cortana that led him to the exit. There, he learned her plan: a replacement for Installation 04 had been built by the Ark, and was not yet connected with the rest of the Array. Since the Halo was so far from the inhabited galaxy, John decided to activate the ring and destroy the Gravemind, but first headed to the remains of High Charity.

"You know me. When I make a promise..."

- John-117

"You...keep it. I do know how to pick 'em."

- Cortana

On High Charity, John battled his way through hordes of Flood, being taunted with images of Cortana falling into rampancy and by threats from the Gravemind. He finally reached Cortana, who still had the Activation Index from the first Installation 04. John then destroyed the city by overloading its backup generators. On his way out, Cortana detected a friendly contact, which turned out to be Thel 'Vadam. High Charity exploded as the trio narrowly escaped on a Pelican.

Firing replacement Installation 04
The final task for John, 'Vadam, and Cortana was to destroy the Flood by activating the replacement Installation 04. The three landed on the Halo, finding that the Gravemind was trying to rebuild itself on the Installation. Flood Dispersal Pods released Combat Forms against John and the Arbiter, forcing them to fight their way up to the Control Room, where the ring could be activated. During the battle, Sergeant Johnson arrived and assist the Chief in battle.

After defeating all Flood forces around the Control Room, 343 Guilty Spark unlocked the door to the Control Room. Once inside, however, Guilty Spark realized that the team intended to fire the Halo before it could be completed, which would destroy the ring. After mortally wounding Sergeant Johnson, he then turned on John.

"You are the child of my makers. Inheritor of all they left behind. You are Forerunner. But this ring...is mine."

- 343 Guilty Spark, betraying the Master Chief

John stood his ground, even after being hit by several energy blasts, and fought against Guilty Spark. Although the Monitor seemed to be invulnerable, Johnson shot the Monitor, temporarily distracting him. He then handed John his Spartan Laser, and John destroyed Guilty Spark. Johnson's injury was fatal, and he requested that John "send [him] out with a bang," after handing over Cortana's data chip and imploring him, "Don't ever let her go."

Cortana then activated the second Installation 04, and the survivors fled to the Forward Unto Dawn onboard a Warthog, fighting the Flood and local Sentinels on the way. The team boarded the Dawn and escaped the firing and destruction of the replacement Installation 04. However, the Slipspace portal opened for them could not sustain itself under the stress, and its closure severed the ship in half, sending 'Vadam to Earth. John and Cortana were left drifting in unknown space.

Missing in action
"But you did it. Truth, and the Covenant...the Flood. It's finished."

- Cortana to John-117

John and Cortana were presumed dead when they did not make it back to Earth. The forward half of the Forward Unto Dawn, bearing the Arbiter, crash-landed on Earth. Lord Hood commissioned a memorial near Mount Kilimanjaro in Africa in honor of UNSC servicemen lost during the war. As there were no pictures to remember him by, John's SPARTAN ID number, 117, was carved onto the memorial by an unknown party, and the UNSC Master Chief Petty Officer of the Navy insignia patch was taped beside his ID number. Ironically, he and a few other Spartans are the only ones truly Missing In Action.

Stranded in space
"Wake me...when you need me."

- John's last words to Cortana

John and Cortana managed to survive the explosion of Installation 04B in the remaining cargo portion of the Forward Unto Dawn, but it was nearly powerless and, without airlocks or a bridge, could not be properly navigated. Cortana, relieved that John had survived, explained this to the Chief, and that it could take years before anyone could discover their distress signal. In a similar conversation to one at the end of Halo 1, Cortana listed what John did and told him "it's finished," and this time, John agreed with her. John placed himself in a cryotube, at which point Cortana said, "I'll miss you." John replied with "Wake me...when you need me."

In 2556, while still stranded in space, Cortana attempted to talk to John while he was still asleep. Unable to get a response from him, she recounted the history of the galaxy, seemingly unaware that John could not hear her, and showing major signs that she was descending into rampancy.

John was last seen in the back half of the Forward Unto Dawn, approaching an unidentified planet.

Personality
"I guess some of your luck has rubbed off on me"

- Dr. Halsey

"We make our own luck, but I'll always be there when you need me."

- John-117

John's personality is explored much more deeply in the books than the games, so players can more easily project their own personalities onto the Master Chief.

As a defining character trait, John strives to win at any situation, at all costs. This seems to have been a part of his character even prior to his conscription to the Spartan program, as he used to win at any game he played, including chess, gravball or King of the Hill. He is extremely determined to complete the mission at hand, and often disregards his personal safety and relies on his abilities and alleged exceptional luck. Indeed, he has often emerged victorious from situations many would consider impossible. Still, he is not devoid of fear, but he simply acknowledges the feeling and puts it aside, never showing it. John is generally stoic and taciturn, but not devoid of a sense of humor. He often makes dry remarks about the situation in hand; however, this seems to be more frequent when interacting with Cortana than anyone else, such as the other Spartans.

One thing that was noted is that John tends to keep his word when he gives it to someone. As he was forced to leave Cortana behind on High Charity, John promised to come back for her after dealing with the Prophet of Truth, but Cortana told him not to make a promise like that when he knew he couldn't keep it. However, John did keep his promise, pointing out that he always did to Cortana saying "you know me: when I make a promise..." cauing Cortana to respond "you keep it," which seemed to give her strength as she gathered herself quickly when before she was somewhat depressed and hopeless while talking to him.

John holds a personal respect for his trainer and mentor SCPO Mendez, as well as Dr. Halsey, who he considers a mother-like figure.

John appears to deny Halsey's claims about his extraordinary luck at several points in Halo Legends, "The Package".

John posseses a deep friendship with the AI Cortana who was assigned to him for his mission to capture the Covenant Prophets. Despite some inital hesitation towards working with an AI out of fear of conflicting directives, John and Cortana quickly formed a formidable team and John realized quickly that Cortana would be a great help instead of a liability. The two's relationship evolved from a partnership to a close friendship over the course of the Halo 1, probably due in part to all of the time the two spent with each other. During their adventures, John showed absolute trust in Cortana, believing in her when even Lord Hood was unsure of her reliablity, even willing to trust her enough to risk Earth on her word that she had a way to stop the Flood. The two also had similar personalities in some areas: they both had a perpensity to blow things up with John commenting at one point he wasn't sure which one of them was better at it and also tended to come up with crazy plans. After Cortana told John his plan to use a Covenant bomb to blow up a Covenant Carrier was crazy, he offered her to remain behind, but she simply responded with "unfortunatly for us both, I like crazy" and during the series, was shown to have some pretty crazy plans of her own.

John is known to show an exceptional care for soldiers under his command. An example of this is during the Battle of Installation 04. When searching for the survivors of the Pillar of Autumn's crash, Fitzgerald was wounded by an Unggoy Needler. John-117 retrieved a first aid kit and "expertly" treated the wound, before asking the Marine if he was okay, showing that he does have a degree of care and sympathy for soldiers under his command, even if he does do a good job of concealing his feelings. Another example is after Sergeant Avery Johnson is killed by the Monitor at the conclusion of Halo 3.

Age
John's age is affected by the same ambiguities as all beings who undergo extended voyages through space. By technical human Earth years, John is approximately 41 years old at the time he crash-landed on Installation 04, and 45 years old in 2556. However, during the 27 Earth years that he has spent fighting the Covenant, considerable time was spent in Slipspace. The aging process is slowed in slipspace by deep sleep in cryo-chambers; in which cellular aging can be halted almost completely. Also, one could expect that individuals participating in slipspace travel might be subject to the timedilation associated with travel at relativistic speeds, so there could be more discrepancy involved there as well.

Appearance
John-117's face has never been seen in the games, and therefore his appearance is left mostly to one's imagination. The novels Halo: The Fall of Reach and Halo: The Flood give some insight to John's appearance. Early in Halo: The Fall of Reach, when Dr. Catherine Halsey and Lieutenant Jacob Keyes go to Eridanus II to observe John as a child, he is described as "a typical six-year-old male, with tousled brown hair and a sly smile that revealed a gap between his front teeth". In Halo: The Flood, referring to John in 2552, he is described as having "Short hair, with serious eyes, a firm mouth, and a strong jaw." He is described as being unnaturally pale, a consequence of spending most of his time in his armor.

In the ending cutscene of Halo: Combat Evolved, John takes off his helmet, and the camera pans upward, leaving the head obscured by the ship window frame as he sets the helmet to his side. Some people have used Halo: Custom Edition development mode to move the camera. However, Bungie's 3D artists did not produce a separate character model for this occasion, just a separate helmet model; if the animation is viewed from inside the ship, it appears as if John takes off his helmet, revealing an identical helmet underneath. Players have also found an Easter Egg in the Halo 3 Beta. Using a Mongoose, players can reveal what looks like a face in a Spartan's helmet. However, Bungie has confirmed that this is Marcus R. Lehto's face, not John's.

For the first time, John's face was shown without a helmet in Halo: Helljumper Issue 1. The comic illustrated the fight between John and four ODSTs. As expected, his face is seen from the side and is covered up in shadow, hiding any specific facial features.

John's face can be seen clearly on the front cover of Halo: The Fall of Reach - Boot Camp Issue One as a six year old child.

Part of John's face could be seen in the Halo 3 dashboard pack on one of the tabs, where his visor colour was transparent. He was shown to have a scar on his right eye.

Trivia

 * John-117 is voiced by Steve Downes in the Halo trilogy and in Halo: Reach's Firefight mode.
 * Fans have many theories as to the significance of his number, 117. Inside the Halo Universe the number was randomly assigned, but Bungie's choice has been theorized upon in many ways. For more, see List of Biblical References in Halo. It was possibly chosen for its mathematical connections to 7, Bungie's favorite number, since $$1\times1\times7=7$$ and $$7^6=117649$$. John 1 Chapter 1, Verse 7, is a passage referring God who relinquished all evil from the world so people could believe, hence 'Believe' being part of the advertising campaign for Halo 3. Additionally, the song Remembrance is 1:17 in length, as well as Prepare to Drop. It is interesting to note that in the year 117, a man named "John I" became the 7th Bishop of Jerusalem. This covers both his name, John-117, and Bungie's apparent love for the number 7. It could also be probable that John-117 is named partially in honor of "John Spartan," protagonist of the movie Demolition Man, who was kept in cryogenic storage as "Prisoner 117" for forty years. It could just also be a play on James Bond's number, 007. Or even a reference to the 1998 alien invasion TV series First Wave, whose main character was referred to as "Subject 117".Or possibly because 77 secounds in minutes is 1:17 minutes.
 * In both Halo: Uprising and Halo 3, John is referred to as Sierra-117. This is a military-appropriate identifier using the Phonetic Alphabet.
 * Bungie's refusal to show John's face has been parodied many times in popular culture.
 * A wax sculpture of the Master Chief can be visited at Madame Tussaud's, L.A. and in Amsterdam. He was the first video game character to become a Madame Tussaud's wax sculpture.
 * Fable II makes a reference to the Master Chief with a character of legend named "Hal", also called the Minstrel Chief. The armor featured (clearly inspired by Halo's MJOLNIR Powered Assault Armor) is known as "Hal's Armor". The Energy Sword also makes an appearance as one of the first weapons you can attain with the Collector's Edition of Fable II. The Assault Rifle can be acquired on the Knothole Island DLC as "Hal's Rifle", and has the largest magazine of any ranged weapon in the entire game, although its damage is low to average. In addition, with the Special Edition, the player can obtain the title "Master Chief" for their hero for free from any title vendor.
 * At Comic-Con 2010, Frank O'Connor hinted that future media featuring the Master Chief after the events of Halo 3 may be produced.
 * Master Chief is never referred to as the 'best' SPARTAN-II, simply the 'luckiest' and only by Dr. Halsey
 * In the Halo: Reach level "The Pillar of Autumn" it is possible to see a quick glance of a Spartan that may be John during the end cutscene. Holding the right thumbstick to the right during the hanger scene will reveal the Spartan in a cryo-chamber. This may alternatively be Linda-058.
 * When previewing John's voice in Halo Reach Firefight, he will reply with references to the Halo Trilogy.
 * "John" is one of the name options for customized Loadouts in Halo: Reach, along with the members of Noble Team and several SPARTAN-II's.
 * In an episode of American Dad when Steve is in the hospital after and accedent, the person in the other room's bed name is John and the room number is 117, probally a reference to John-117