The Reapers are a fictional fleet of sentient starships that serve as the main antagonists of the Mass Effect trilogy. The design of the Reapers was inspired by H. P. Lovecraft's Cthulhu Mythos deities. Within the series, the Reapers are cosmic horrors that cause galactic-level mass extinctions every fifty-thousand years. The Reapers have never once needed to "defeat" a civilization that they could persuade to surrender itself; they and their technology are capable of brainwashing organic life, and true synthetics subverted through digital means, through a mind control process called indoctrination. The Reapers employ servants who are often altered into synthetic-organic life forms. The Citadel at the heart of the relay system is a massive trap set by the Reapers; they guide rising civilizations along the same technological paths and encourage them to set up a central government on the Citadel itself. All this makes it much easier for the Reapers to harvest the galaxy, because everyone is dependent on the relays that they control.