Sillarc was a reptilian humanoid who once tried to steal a TARDIS from Gallifrey.
His plan involved using an hypnotic device to distract the Time Lords while he stole a TARDIS. He wanted to use the stolen time capsule to plunder all of time and space.
The TARDIS he chose was being repaired by Plutar and could only move in time, not space. Thus, he was only able to transport himself and the unsuspecting repair technician back to Gallifrey's distant past. There, two Gargantosaurs fought one another near the TARDIS and picked up and moved the TARDIS in their battle. After narrowly escaping being killed by Sillarc, both of them rushed to the TARDIS. Plutar tried holding the door closed, but Sillarc broke in. The pair landed close to the Time Lords who were distracted by Sillarc's hypnotic image as he secretly stole the TARDIS and Sillarc was forced to take off again. When Sillarc attempted to transport the TARDIS on board his spacecraft, Plutar and armed guards were waiting for him and he was arrested. His memories were wiped and he was banished from Gallifrey. (COMIC: The Stolen TARDIS)