User blog comment:Simi truck/spoiler warning! final boss on me2/@comment-1878375-20100210150543

My guess on that, is that the Reapers were someone's ships once upon a time, and just like EDI was given control of the Normandy, the Reaper's creators let AI run the ships. It just spiraled out of control from there, just like the Geth did, and now they're a extinction force of nature that uses liquefied organics to produce more Reapers.