Halo: Combat Evolved, also known as Halo: CE, Halo 1, or simply Halo, is a first-person shooter video game developed by Bungie and published by Microsoft Game Studios. The first game in the Halo franchise, it was released on November 15, 2001 as a launch title exclusive to the Xbox game system[1] and is considered the platform’s “killer app”.[7] As of November 9, 2005, over five million copies had been sold worldwide.[8] Microsoft released versions of the game for Microsoft Windows (ported by Gearbox Software) and Mac OS X in 2003, and the surrounding plot has been adapted and expanded into a series of novels, comics, and online short films. The game was later released as an Xbox Original for download to the Xbox 360 hard drive. Halo is set in the twenty-sixth century, and the player assumes the role of the main boss, a cybernetically enhanced super-soldier. The player is accompanied by Cortana, an artificial intelligence who occupies the driver’s main neural interface. Players battle various aliens as they attempt to uncover the secrets of the eponymous Halo, a ring-shaped artificial world. The game was praised for elements such as the story, the variety of strategies used by players, and the multiplayer mode; however, critics often criticized the repetition of its level design.