The Master Chief, originally named John, was born in March 7 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.
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.
At the age of fourteen, John underwent the dangerous SPARTAN-II augmentation procedures. These procedures killed 30 and physically disabled 12 of the Spartan trainees. John was one of 33 Spartans who survived the process unscathed, while the rest who could still operate were moved to positions in the Office of Naval Intelligence. the augmentation process hastened their reflexes, increased their strength, enhanced their eyesight, and rendered their bones nearly unbreakable. After their augmentation procedures, John and the other Spartans were transferred to the Atlas in order to recover in a microgravity environment
After the augmentations, John and the other spartans were equipped with The Mjolnir Powered Assault Armor (MPAA, or simply Mjolnir) is a technologically advanced combat exoskeleton system designed to vastly improve the strength, speed, agility, reflexes and durability of a SPARTAN-II, SPARTAN-III or a SPARTAN-IV supersoldier in the field of combat. The suit also possesses other features that enhance its wearer's abilities. It has numerous clips, belts, and magnetic holsters for the attachment of additional weapons and ammunition; an advanced Heads-Up-Display(HUD) linked to sensors in the gloves detects the type of weapon and devices held, and to project shield strength, ammunition count, a targeting reticle, waypoints, a radio uplink for communication, health monitoring and other helpful data.
Although initially the spartan II program was designed to neutralize human rebel insurgence in the outer colonies and those who opposed the UNSC and central government, A new enemy would emerge shortly after the near completion of the program, they were known as the covenant, a collection of alien species, rallied under one banner based off of their religion, searching for ancient artifacts to progress their great journey, humanity was caught in the cross-fire of this campaign and were plunged into the human-covenant war for nearly three decades.
The Master Chief throughout the human-covenant war, would often be deployed on the frontlines and deep into enemy territory, to sabotage Covenant war machines, factories, supply lines, etc. John along with the few remaining Spartan II’s would go on to being one of the most important figures in the human-covenant war, killing off major covenant leaders, important military figures, and destabilizing covenant military command, weakening their chain of command, and eventually with the aid of several allies, dissolving the covenant as a whole.