A lot of pooples don't seem to know what a Forerunner is or what their role was in the Halo Universe so help me explain. What I know I learned from reading, watching Origins I and II, and talking to Halo Fans. The Forerunners were(or possibly are) a very advanced civilization. The most advanced civilization that humans have ever thought of. They created the Halo Rings to stop The Flood from controlling all sentient life in the Galaxy, at the cost of all life in the Galaxy, including their own. but they prepared for this mass slaughter and re-populated the planets with the same species that originally inhabited them, save their own species. The chief blew up one of the Halo Rings(Alpha Halo) but it turned out there was a replacement. The Forerunners are awesome like that.