The Derivitrons were a race of robots created by Tabon who, against his will, completed his project to build the Perfect One. They remained in a building on Luxor and killed those who entered and refused to give up their own lives.
They were programmed to be aware only of Luxor and, as a result, Proto did not believe the claims of the First Doctor, Susan Foreman, Ian Chesterton and Barbara Wright. They went berserk when Tabon and the Perfect One gave them conflicting orders and were destroyed when the complex exploded. (AUDIO: The Masters of Luxor)