Reaper

The Reapers are a highly-advanced machine species of synthetic-organic starships. The Reapers reside in dark space: the vast, mostly starless space between galaxies. They hibernate there, dormant for fifty thousand years at a time, before returning to the galaxy.

These giant machines are ancient; their true name is unknown. "Reapers" was a name bestowed by the Protheans, the previous galactic power fifty thousand years before, and the Geth refer to them as the Old Machines. In the end, the Reapers spare little concern for whatever labels other races choose to call them, and merely claim that they have neither beginning nor end.

The Reapers are the original creators of the Citadel 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.

History
Origins= The Prothean Counterattack=

Culture
The Cycle of Extinction= Harvesting=