Mitzi

Mitzi was a cat that had been sent into hyperspace by some human scientists.

She landed on a planet that had been terraformed and later the humans inhabited it. She took control over the humans and they where forced to serve her. Ninety years later, the Doctor and Rose Tyler landed on the planet that she ruled.

The Doctor confronted her and persuaded her to go and step down. Mitzi then took a trip in the TARDIS and was sent to the Powel Estate. Rose told the Doctor that she found Mitzi and renamed her in her past. She would have lived for another five years under the Tyler family's care. (DWA: The Cat Came Back)