If you want a fierce or intimidating sounding name, I'd suggest Killer or Zodiac (after the Zodiac Killer).
If you want a name that sounds fierce, ruthless, and a little silly, name the cat Chairman Miao. (It's what I called my brother's cat, because he was an evil dictator a la Mao, except the name's Miao because he's a cat. He actually answered to that name, too.)
If you want a name that's literary and a little silly, I'd suggest Percy, after Percy Bysshe Shelley, a fantastic poet and great intellect, but by most accounts not a very nice guy. His fame was (deservedly, IMO) eclipsed by that of his wife Mary, who wrote Frankenstein.
And if we want to go scary but silly, I'd suggest FrankenKitty.