Halo is a multi-billion dollar science fiction video game franchise created by Bungie and now managed by 343 Industries and owned by Microsoft Studios. The series centers on an interstellar war between humanity and a theocratic alliance of aliens known as the Covenant. The Covenant are led by their religious leaders, The Prophets, and worship an ancient civilization known as the Forerunners, who perished in combat with the parasitic Flood. Many of the games center on the experiences of Master Chief John-117, a cybernetically enhanced human super-soldier, and his artificial intelligence (AI) companion, Cortana. The term "Halo" refers to the Halo rings: large, habitable structures that were created by the Forerunners to destroy the Flood. They are similar to the Orbitals in Iain M Banks' Culture novels, and author Larry Niven's Ringworld concept.