Master Chief may refer to:

Military rank

Positions

Fictional characters

MCPON John-117, or "Master Chief", is a fictional character and the protagonist of the Halo fictional universe created by Bungie. Master Chief is a playable character in the series of science fiction first-person shooter video games: Halo: Combat Evolved, Halo 2, Halo 3, Halo 4, and Halo 5: Guardians. Outside video games, the character appears in novels— Halo: The Fall of Reach, Halo: The Flood, Halo: First Strike, and Halo: Uprising —and has cameos in other Halo media, including Halo: Reach, Halo: Ghosts of Onyx, The Halo Graphic Novel, Halo Legends and Halo 4: Forward Unto Dawn.

The character is a towering and faceless biochemically and cybernetically-enhanced supersoldier, raised and trained from an early age to be a weapon; he is almost never seen without his green-colored armor and helmet. He is commonly referred to by his naval rank, rather than his given birth-name or serial-designation. The character is voiced by Steve Downes, a Chicago disc jockey, in the video games in which he appears. Downes based his personification of the Chief on an initial character sketch which called for a Clint Eastwood-type character of few words.