Roboman
Robomen were humans converted by the Daleks into wholly-obedient slaves during the 22nd century Dalek invasion of Earth. These surgically-modified captives were used for patrols and overseeing other slaves. The so-called "Robomen" were needed because there were relatively few Daleks on Earth.
The Daleks captured prisoners and operated on their brain in a surgical procedure called the Transfer, plus fitting them with large helmet-like headsets. The mind control technique the Daleks used was unstable, and the Robomen would eventually go insane and commit suicide. (DW: The Dalek Invasion of Earth)
A more sophisticated implantation technique was revealed after the conquest of Vega 6. Rather than fitting their subjects with grafted positronic discs and communication devices, the circuitry was placed inside the brain itself and the Robomen retained independent thought. Due to this, they were much harder to detect and considered far more dangerous. Orders from their Dalek masters would be filtered within normal thought processes, the subject seemingly unaware of the disc implant. One such Roboman was Gordon Pellan, who was gunned down by Earth Alliance forces. (BFDE: The Human Factor)
