The Reapers are an army of machines that arrive every few millennia to eradicate and harvest all advanced organic species. They reside in dark space, which is devoid of stars and galaxies. They are extremely advanced, and created the mass relays and the Citadel. The Reapers can supposedly be destroyed or controlled by a weapon known as the Crucible, which has never been completed by any sentient organic race before this cycle. Notable Reapers include Sovereign, who led the attack on the Citadel, and Harbinger, who leads the Reapers.
