Master Chief

The Master Chief, originally named John, was born in 2511 and first lived with his family on the human colony planet Eridanus II. Large for his six years of age, and approximately a foot above his school peers, he is described as a typical boy with brown hair, freckles and a gap between his two front teeth.In 2517, John and seventy-four other children his age are covertly taken from their homes and replaced with clones to hide the kidnapping. The original children are brought to planet Reach, one of the UNSC's headquarters, to begin intense physical and psychological training to become SPARTAN-II supersoldiers. They are assigned new identification numbers instead of last names; John becomes known as John-117. Approximately eight years later, John and the other children are biologically and cybernetically augmented and enhanced. These procedures had substantial risks;[17] only John and thirty-two other Spartans survive.

After the Spartans' first successful operation which involved capturing a rogue UNSC officer, John-117 is briefed on the threat posed by the Covenant, a theocratic alliance of alien races, and witnesses the utter devastation wrought by a single ship. The Spartans are first sent to the Damascus Materials Testing Facility on the planet Chi Ceti 4 to retrieve the MJOLNIR Mark IV armor. In the process, they board a Covenant vessel and plant a bomb; John is forced to leave one of his fellow Spartans, his best friend, to die.

In 2552, the Covenant invades the human world of Sigma Octanus and occupies one of its cities, Cote D'Azure. Following a failed Marine assault, John-117 and three teams of Spartans are sent to destroy the Covenant force with a nuclear warhead. After detonating the weapon, the Spartans return to Reach, where the UNSC High Command has developed a last-ditch plan to capture a Covenant High Prophet, who they hope could be used in order to barter a truce.[17] The Master Chief's armor is upgraded, and he first encounters the artificial intelligence (AI) Cortana during a training mission.[17] A massive Covenant armada of 314 ships arrives and begins to destroy the planet, despite the best efforts of the Spartans and other UNSC forces. Aboard the spaceship Pillar of Autumn, Cortana plots a random course of escape.Seemingly the last Spartan alive, the Master Chief enters cryonic sleep along with the Pillar of Autumn's crew.

Born in about 2511, John lived with his mother and father in Elysium City, on the colony world of Eridanus II. He attended to 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."[4] At the age of six, he was identified by Dr. 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 strength, exhibiting 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", 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 Reach. Dr. Halsey informed them of the SPARTAN-II Program and how they would be the protectors of Earth and her 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 be the only close friends he would ever have.

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. 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 up, 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, and in addition to the fact that the Spartans may have never seen Marines before, therefore mistaken for a hostile threat. John showed early acumen in critical thinking and tactics, not wishing to take it 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 attacked his Marines and also, no one had been left behind. But both he and Dr. Halsey recognized John's initiative, and promoted him to Squad Leader. After this, despite the 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.

At the age of 14, John underwent the dangerous process of SPARTAN-II Augmentation Procedures that caused almost half of the Spartan candidates to die, or be 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.