Master Chief is the protagonist in the Halo game series and spin-off media. Also known as Master Chief Petty Officer John-117, the character appeared in the 2001 video game Halo: Combat Evolved, a science fiction first-person shooter that became a long-running video game series. The character also appears in spin-off Halo media such as the 2012 film Halo 4: Forward Unto Dawn, the 2022 Halo television series, and several graphic novels and books.

Halo is a military science fiction media franchise, originally developed and created by Bungie and currently managed and developed by 343 Industries, part of Microsoft's Xbox Game Studios. The series launched in 2001 with the first-person shooter video game Halo: Combat Evolved and its tie-in novel, The Fall of Reach. The latest main game, Halo Infinite, was released in late 2021.