Quadrigger

Quadriggers were engineers on Gallifrey who worked on TARDISes. Stoyn was a Quadrigger who was working on decommissioning the Doctor's TARDIS when the First Doctor stole it. (AUDIO: The Beginning)

Quadriggers were set to work on a TARDIS stolen by the Master when he first left Gallifrey. (AUDIO: The Destination Wars)