The Rovie was originally a normal rovie which lived around the Citadel. He had an ordinary life, avoiding the Time Lords and their cleaning machines. When the Doctor came to Gallifrey on a mission, the Rovie hid in his TARDIS. There he lived for many years, with the TARDIS protecting and feeding him. When a remote operation module was installed by Shayde, there was a leak from a temporal relay, exposing the Rovie to the Time Vortex. Instead of being aged to death, the TARDIS tried to protect him, causing him to evolve thousands of years in minutes. He was increased ten times in size, while his brain was increased a thousand times in size. He was able to tap into the TARDIS' memory banks and learn from it. Despite this, he was unable to develop any social skills and was insane.
He lived alone in the TARDIS for years, having no one to talk to. The Rovie planned to return to Gallifrey and use the same process on other rovies. With them and the technology of Gallifrey, they could then take over the universe. To this end, he found the dimensional induction chamber, where he built a device to take control of the TARDIS and its interior. He also set up defences to protect him, such as a force field. He used his control of the TARDIS to try to kill the Fifth Doctor and Erimem, opening the TARDIS into the Time Vortex. Shayde was sent to help the Doctor and stop the Rovie, but Shayde was trapped by the Rovie in a force field. When the Doctor and Erimem finally found the Rovie, they were unable to take him seriously, still being a rodent. They were able to provoke him with mouse-based insults, which caused him to leave his force field to attack. Erimem then smashed Rovie's machine, freeing Shayde and allowing him to capture the Rovie. Shayde planned to return the Rovie to Gallifrey for study. (AUDIO: No Place Like Home)