10 Times Supervillains Killed Other Villains
9. Joker Kills Alexander Luthor - Infinite Crisis
It shouldn't come as any surprise to learn that the Joker has killed a villain or two in his time. The man is obsessed with having Batman all to himself and he's said repeatedly he doesn't believe there's any room for competition. It's what's led to several of the Dark Knight's villains falling into his crosshairs on more than one occasion.
And while villainous alliances are fragile at the best of times, every villain knows not to depend on the Joker. He's too chaotic, as brilliant as coming up with schemes as he is liable to decide everything is boring, and go off and do something dramatic.
He's a serial double crosser and one with no proclivity towards preserving human life; if you tick him off, or just happen to be in his path - even if you're a henchman, as Batman 1989's Bob unluckily discovered - there's a solid chance he's going to kill you just for the hell of it.
The Joker can also be extremely deliberate with his violence however, as was the case with 2005's Infinite Crisis.
Following Alexander Luthor Jr's attempts to remake the multiverse into one "perfect" reality, he finds himself cornered by the Lex Luthor and Joker of New Earth (aka the mainstream DC continuity). Joker scars Luthor Jr with acid, and then brains him with a gun - all because the alt-Luthor didn't include him in his scheme in the first place.