Master Chief Petty Officer John-117, commonly called the Master Chief, is a fictional character and the main protagonist of the Halo universe, created by Bungie Studios, and is a playable character in the trilogy of science fiction first-person shooter (FPS) video games Halo: Combat Evolved, Halo 2, and Halo 3. Outside of video games, the Master Chief appears in the novels Halo: The Fall of Reach, Halo: The Flood, Halo: First Strike, and Halo: Uprising, and has cameos in Halo: Ghosts of Onyx and the Halo Graphic Novel. He is voiced by Chicago disc jockey Steve Downes in the video games in which he appears.

The Master Chief is one of the most visible symbols of the Halo series and the video game universe. Originally designed by Marcus Lehto, Rob McLees, and Shi Kai Wang, the character is a towering and faceless cybernetically enhanced supersoldier; he is never seen without his green-colored armor or helmet. Downes built his personification of the Chief off a character description which called for a Clint Eastwood-type character of few words.

The Master Chief has been called an icon, a relative newcomer among more established franchise characters, such as Mario, Sonic the Hedgehog, and Lara Croft.[1] While a widely known figure, the Master Chief has received mixed reception. Reviewers such as Kotaku have pointed to the Chief's silent and faceless nature as a weakness to the character, while other publications have stated that this attribute allows players to better assume the role of the Master Chief.

(I got this information off of wikipedia)