Halo is a science fiction video game series created by Bungie Studios. The series centers on the Master Chief, a cybernetically enhanced human super-soldier equipped with technologically-advanced battle armor, and his artificial intelligence (AI) companion, Cortana, as the humans of a futuristic universe battle the Covenant, a theocratic alliance of alien races. In this science fiction setting, the term "Halo" refers to the Halo megastructure, a large orbital construction, similar to those first popularized by the 1970 novel Ringworld by Larry Niven, though smaller in scale.
The video games, particularly Halo: Combat Evolved, have been praised as being among the best first-person shooters on a game console, with Halo being the Microsoft Xbox's "killer app". This has led to the term "Halo killer" being used to describe console games that aspire to be better than Halo. Halo's sequel, Halo 2, broke sales records for a media release, and Halo 3 sold more than US $170 million worth of copies in the first 24 hours of release, breaking the record of Halo 2. As of October 4, 2007, all three Halo games combined have sold more than 20 million copies. The franchise has expanded to include five novels, several graphic novels, and numerous other licensed products, from action figures to Mountain Dew. The cultural impact of the Halo series has been compared by Brian Bendis to that of the Star Wars franchise, and with those who enjoy the series being dubbed the "Halo Nation".