The Reapers were the original creators of the Citadel space station and the mass relay network. These massive constructs exist so that any intelligent life in the galaxy would eventually discover them and base their technology upon them – all part of a scheme to harvest the galaxy’s sentient life in a repeating cycle of purges that has continued relentlessly over countless millennia. This cycle of death was ended at the end of the third game in the series, almost always costing the player character's life.