Graymalkin, Jill the Witch's familiar and accomplice of Snuff, from the novel A Night In The Lonesome October[?] by Roger Zelazny, (a graymalkin or grimalkin is an old or evil-looking she-cat)
The film Cats & Dogs[?] postulates an ongoing war dating back to ancient times between cats and dogs. The most notable cat is a spoilt Persian called Mr. Tinkles who is also an evil genius.
Blofeld's unnamed cat from the James Bond movies, which has inspired a number of imitations and spoofs (see Mr Bigglesworth, Madcat, and Nero)
Nero, a fluffy white caterpillar, pet of the villainous toad Silas Greenback, from the cartoon series Danger Mouse[?] -- a parody of Blofeld's cat (see above)
Schrödinger's cat, hapless victim (or lucky survivor) of a thought experiment by Erwin Schrödinger illustrating the incompleteness of the theory of quantum mechanics (although Schrödinger himself is historical, the cat is the protagonist in a thought experiment and thus fictional)
... wrongs of the past, they don't call themselves quacks, they can change their name to whatever is trendy at the time, e.g. herbalist. They also promote the distrust of ...