Master Chief Petty Officer of the UNSC Navy, John-117 is a SPARTAN-II Commando of the UNSC Naval Special Warfare Command. With nearly 30 years of active duty, he is one of the most decorated soldiers in the United Nations Space Command and has earned every known medal in the UNSC except the Prisoner of War Medallion. In 2553, John-117 went missing in action after the Battle of Installation 00 when he and the current Arbiter Thel 'Vadam slowed (as Gravemind had say) the Flood threat
He is more commonly known as, "Spartan" by Thel 'Vadam and Rtas 'Vadum, "Demon" by the Covenant and other Sangheili until the Covenant Civil War, after which the other Sangheili also started to refer to him as "Spartan", "Master Chief" and "Chief" by Humans, and "Reclaimer" by both 343 Guilty Spark and 2401 Penitent Tangent.
He is the protagonist and a playable character of Halo: Combat Evolved, Halo 2, and Halo 3.