Character from The Dresden Files by Jim Butcher
The Elder Grimalkin of Winter — a talking cat the size of a bobcat who serves as Mab's premier assassin with the courtesy of a butler and the lethality of a cruise missile.
Cat Sith is the Elder Grimalkin — the lord of the malks, Winter's supernatural cats — and he serves Mab as personal assassin, spy, and occasional liaison. He speaks with precise, formal diction and impeccable manners that make his death threats sound like polite suggestions. He is extraordinarily dangerous; even other Winter Fae treat him with careful respect. His service to Harry as temporary aide was conducted with barely concealed contempt for Harry's lack of subtlety, delivered through the kind of cutting observations that only a cat could make sound natural. He was eventually compromised by Nemesis during the events of Cold Days, forcing Harry to destroy what may have been one of Winter's most valuable assets.
A large, sleek black cat — bigger than a housecat, closer to a bobcat — with luminous green eyes that hold an intelligence far beyond animal. His fur seems to absorb light. Moves with absolute silence, appearing and disappearing at will. His form is deceptively domestic; there's something in the way shadows gather around him that suggests the cat shape is a courtesy, and what's underneath is considerably larger and more dangerous.
Also known as: Cat Sith, Elder Grimalkin, Sith