Dr. Gavin Archer is the true main antagonist of the Overlord DLC in Mass Effect 2. He was a Cerberus scientist who run a Cerberus Project called "Overlord". This project was a means on how to control the geth. After observing his autistic brother, David's intelligence and ability to communicate with them, he had him forcibly incorporated to the Geth VI to figure out a way to control the Geth. The experiment eventually went horribly wrong due to David's mental instability and the torture. The Geth had gone berserk and started killing the Cerberus staff, until the two brothers were the only survivors.