Halo figurine Nendoroid Master Chief 10 cm

Master Chief Petty Officer of the UNSC Navy, John-117 is a SPARTAN-II Commando of the UNSC Naval Special Warfare Command.

John was taken away from his homeworld Eridanus II and trained to become a Spartan from the age of six. He and 32 other recruits passed SPARTAN-II program. In the process he was augmented mechanically and biologically.

His augmentations include:

1.Ceramic grafting onto bones, making them virtually unbreakable.
2.Muscular Enhancement.
3.Increased Human growth.
4.Visual Enhancement, with the ability to see clearly in the dark.
5.Superconducting fabrication of neural dendrites: alteration of bioelectrical nerve transduction to shielded electronic transduction. Three hundred percent increase in subject’s reflexes. Anecdotal evidence of marked increase in intelligence, memory and creativity.

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.

He is more commonly known as "Spartan" by Thel and Rtas 'Vadum, "Demon" by the Covenant and other Sangheili, "Master Chief" and "Chief" by Humans, and "Reclaimer" by both 343 Guilty Spark and 2401 Penitent Tangent. Barely anyone calls him "John" except for Dr Halsey and Cortana.