Rat

The fancy rat is a domesticated brown rat (Rattus norvegicus), which is the most common type of pet rat. The name fancy rat derives from the idea of animal fancy or the phrase "to fancy" (to like, or appreciate).
Pet rats have their origins as the targets for blood sport in 18th and 19th century Europe. Specially bred as pets since then, fancy rats now come in a wide variety of colours and coat types and there exists several rat fancy groups worldwide. Fancy rats are commonly sold as pets in stores and by breeders. In fiction, pet brown rats tend to be depicted as tamed rather than domesticated, akin to when a character befriends a wolf. As tamed pets, they have played roles that vary from evil, to ambiguous, to lovable.

http://en.wikipedia.org/wiki/Fancy_rat