Which original Xbox game starred Master Chief and was a launch title for the console?

Halo: Combat Evolved starred Master Chief and was a launch title for the original Xbox.

Halo: Combat Evolved was released for Xbox in North America on November 15, 2001, the same day Microsoft's console launched. Developed by Bungie and published by Microsoft Game Studios, it placed players in the role of the supersoldier Master Chief Petty Officer John-117.

The game follows humanity's conflict with the Covenant and the discovery of the mysterious ringworld known as Halo. Its campaign, vehicle sections, weapons, and competitive multiplayer became central examples of console first-person-shooter design.

The subtitle “Combat Evolved” was important because the game was originally known simply as Halo during development. Halo 2 followed in 2004, but it was not the original Xbox launch title. Halo's success also helped turn Master Chief into the best-known character associated with Xbox.