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.