Marmaduke was the name that the Second Doctor gave to a large, cat-like creature that a telepathic old woman, exiled to a bubble universe, created to keep herself company.
The Doctor adopted Marmaduke as a companion aboard his TARDIS. Marmaduke was very mischievous, destroying many things in the TARDIS, including the warm-weather clothing, Jamie McCrimmon's bagpipes, and the TARDIS roundels. Marmaduke also amplified the Doctor's telepathic abilities. When Marmaduke destroyed much of the control room, the Doctor decided to get rid of Marmaduke. After several mishaps, he was able to return Marmaduke to his original owner. (PROSE: Constant Companion)