Master Chief

Master Chief Petty Officer John-117 is a Spartan-II commando of the UNSC Naval Special Warfare Command who became one of the most important UNSC heroes during the Human-Covenant war. With over thirty years of active duty, he has become one of the most decorated war veterans in the United Nations Space Command, earning every known UNSC medal except the Prisoner of War Medallion.

John-117 is the protagonist and main playable character in both the Halo trilogy and Reclaimer Saga. John is only ever referred to by name once in the Halo trilogy of games: by Cortana in the ending cutscene of Halo 3 prior to the credits. In Halo 4 -the beginning of the Reclaimer Saga, both Catherine Halsey and Cortana refer to him by name twice. Humans generally refer to him as the "Master Chief", "Chief" for short, or "Sierra-117". The Covenant, aware of the lethality of the Spartans, refer to John exclusively as "Demon". However, after the Great Schism and the Sangheili alliance with the UNSC, both Thel 'Vadam and Rtas 'Vadum alternatively referred to him as "Spartan". Forerunner enemies and their AI constructs generally refer to John as "Reclaimer", although they seem to use this term in reference to all humans, and not John specifically. Interestingly, the Ur-Didact in his apparent disdain for humanity, chose to curtly address John as "human". However, after John had successfully infiltrated his way into Mantle's Approach, the Ur-Didact chose to refer to him more respectfully as "warrior" before their final confrontation atop the light bridge.

Story
John was born in 2511 on Eridanus II, where he lived in the city of Elysium with family. At the age of six years he was chosen to be part of the SPARTAN-II project, for this was taken from Dr. Halsey and the then Lieutenant Jacob Keyes and replaced by a fast-growing clone. From the beginning it becomes the favorite of the Doctor because of his good fortune, also demonstrated in the simple game launch of the currency, and its abilities. His physical appearance is only known that he has brown hair, serious look, freckles, jaw pronounced, a little space between the upper incisors and as a child was extraordinarily tall and strong, enough to cope with several other children They are trying to conquer the hill where John placed his feet.

Arrived on Reach along with other 74 Program candidates, John began his training supervised by the Chief Franklin Mendez and Déjà AI. From the first day he formed a deep friendship with Kelly and Sam, his teammates. Following a mission in a forest on the mountain ranges of Reach, where John demonstrated his ability to command taking home all the other children, he was appointed head of his team.

At 14, John was subjected to the alteration process and increased capacity, surviving along with 32 other candidates without permanent damage and gaining strength, reflexes, endurance, speed and superhuman sight. To recover from the effects of power-ups, the Spartans were transferred to Atlas. While training in the gym, John was challenged by 4 ODST in close combat, in which 2 Leapers Infernal were killed and two others seriously injured.