Mitzi

Mitzi was a cat that had been sent into Hyperspace by some human scientists. She landed on a planet that had been terafromed and later the humans inhabbited it. She took control over the humans and they where forced to serve her.90 years later the Doctor and Rose Tyler landed on the Planet that she ruled and the Doctor confronted her and persuaded her to go and step down. She took a trip in the Tardis and was sent to the Powel Estate. Rose tells the doctor that she found Mitzi and renamed her. She would lie for another five years under the tyler familys care. (TDA: The Cat Came Back)