The Xbox Space-War Franchise is best known for its flagship title, HALO. HALO is a science fiction first-person shooter video game series developed by Bungie and published by Microsoft Game Studios. The series centers on an interstellar war between humanity and an alliance of aliens known as the Covenant. The Covenant, led by their religious leaders called the Prophets, worship an ancient civilization known as the Forerunners, who perished in combat with the parasitic Flood. The central focus of the franchise builds off the experiences of Master Chief John-117, one of a group of supersoldiers codenamed Spartans, and his artificial intelligence (AI) companion, Cortana. Other characters, such as Noble Six from HALO: Reach, are also introduced in the series.