Robomen were humans converted by the Daleks into wholly obedient slaves during 2025 (AUDIO: Energy of the Daleks) and the 22nd century Dalek invasion of Earth. The Daleks captured prisoners and operated on their brains in a surgical procedure called the transfer, fitting them with large, helmet-like headsets. The Daleks' mind control technique was unstable, and would eventually wear off. However, instead of reverting, i.e. becoming human again, the Robomen would go insane and take their own lives. (TV: The Dalek Invasion of Earth)