Halo is a science fiction video game franchise created by Bungie. The main trilogy of games center on the experiences of the Master Chief, a cybernetically-enhanced human super-soldier, and his artificial intelligence (AI) companion, Cortana. The Master Chief aids future humanity in battling the Covenant, a theocratic alliance of alien races that store a parasitic organisms known as the Flood. In this science fiction setting, the term "Halo" refers to Halo megastructures: large, habitable ringed structures, similar to Larry Niven's Ringworld. The trilogy of video games have been praised as being among the best first-person shooters on a video game console.