Halo 2 is a 2004 first-person shooter game developed by Bungie and published by Microsoft Game Studios for the Xbox console. Halo 2 is the second installment in the Halo franchise and the sequel to 2001's critically acclaimed Halo: Combat Evolved. The game features new weapons, enemies, and vehicles, another player character, and shipped with online multiplayer via Microsoft's Xbox Live service. In Halo 2's story mode, the player assumes the roles of the human Master Chief and alien Arbiter in a 26th-century conflict between the United Nations Space Command, the genocidal Covenant, and later, the parasitic Flood.

Halo: Combat Evolved is a 2001 first-person shooter video game developed by Bungie and published by Microsoft Game Studios for the Xbox. It was released as a launch game for Microsoft's Xbox video game console on November 15, 2001. The game was ported to Microsoft Windows and Mac OS X in 2003. It 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.