Unit Three was the name given to a Scientist Dalek.
Unit Three was captured and taken aboard Station 7. Several Scientist Daleks were part of the platoon led by Chief Strategist that attacked Station 7, with several other Strategists and Drones under its leadership. From the command ship, Scientists transmitted control signals calling all Robomen and Ogrons detained on the station to kill all humans, while others fed static electricity to the station's floors allowing captured Dalek technology to reactivate. (COMIC: The Only Good Dalek)