Halo is a Microsoft Xbox Killer app game, the best in first-person shoot 'em ups. It centers on Master Chief, a cybernetically-enhanced human super-soldier, & Cortana, his AI friend. Master Chief aids humanity in its fight against the alien Covenant alliance, & the Flood parasites. The Covenant worship the Forerunners, an ancient civilization that built the habitable Halo megastructures rings in their fight against the Flood. The Conenant discovered that humans actually descended from the Forerunners, but chose genocide, as a good hush story, over the truth.