Halo: Combat Evolved, simply known as Halo, is a first-person shooter game developed by Bungie and published by Microsoft Game Studios. It was released as a launch game for Microsoft's Xbox video game console on November 15, 2001. Microsoft released versions of the game for Windows and Mac OS X in 2003. The game was later released as a downloadable Xbox Original for the Xbox 360. Halo is set in the twenty-sixth century, with the player assuming the role of the Master Chief, a cybernetically enhanced supersoldier. The Chief is accompanied by Cortana, an artificial intelligence. Players battle aliens as they attempt to uncover the secrets of the eponymous Halo, a ring-shaped artificial world.