The quintessential Halo character. Master Chief Petty Officer Spartan John-117, aka the Master Chief, aka John, has the most impressive record of any UNSC service member in history, and likely any soldier from any time in recorded human history.
The most decorated soldier in the United Nations Space Command, John-117 has fought in more battles, killed more Covenant, saved more lives, and earned more commendations than any other single human being in history. His actions during the Human-Covenant War were responsible for helping humanity survive long enough to eventually turn the tide of the war, and at the end was crucial in defeating the Covenant hegemony. Were it not for the Master Chief, Earth, the UNSC, and all of humanity would likely have been lost.
John was born in Elysium City, a small outer colony located on the planet Eridanus II in the Eridanus system. He lived a relatively normal life until the age of six, when he was kidnapped by the Office of Naval Intelligence for their top secret Spartan-II program. Though not the smartest, fastest, or strongest Spartan, John was widely considered the best leader, and quickly became the de facto top Spartan-II.
John was lost aboard the UNSC Forward Unto Dawn for four years following the Battle of Installation 00, the last engagement of the Human-Covenant War. His return to the UNSC in 2557 was met with immediate conflict, and hasn't stopped since. He was finally reunited with the rest of Spartan-II Blue Team after the Battle of Requiem, and since then has fought to keep the peace in a very uncertain galaxy.
BATTLING THE CREATED
Towards the end of 2558, John and Blue Team became embroiled in the beginnings of the Rise of the Created, nearly getting captured by Cortana. His actions, with the help of the rest of Blue Team and Fireteam Osiris, were successful in the release of Blue Team from Cortana's imprisonment, though the Created were still able to wrestle control of the Galaxy from the UNSC and the rest of the intelligent species that inhabit it.