Dio Brando from JoJo's Bizarre Adventure, particularly in Part III. He has no compunctions forcing people to do his bidding, and even if they do that, it's no guarantee of survival (think the rich man who drives him around in Part III). His shadow also looms large over all antagonists that follow him, with all of them being connected to him in some way, and he's directly responsible for the events of Part VI, where all the main characters die. Oh, and he used his time-stopping stand to force someone to eat a dead cat and stab someone else in the face - and he did this just because he could.
Dio also makes a habit of recruiting other Complete Monstersas minions: Jack the Ripper, Gray Fly, J. Geil, Steely Dan, Alessi, Terence D'Arby (what, you thought "Bizarre" was in the title just for show?)...
Need we mention his manifold heinous acts in Part I? After being adopted by Jonathan's (the protagonist of Part I) father, he proceeds to make Jonathan's life a living hell for no adequate reason. He beats up Jonathan, humiliates his girlfriend, burns his dog alive, tries to poison his father, and even forfeits his humanity to become a nigh-immortal vampire. Things only get worse from here, with Dio embarking on a killing spree across London. Arguably, his single worst act in Part I is cornering a young woman, who begs Dio to spare her baby. Dio agrees, promising not to kill the baby, then kills the woman and revives her as a zombie. True to his word, he leaves the baby...but instead watches as the zombified woman proceeds to eat her own child in front of him. The bastard refuses to die after being defeated, with his severed head returning at the very end to attack the cruise ship Jonathan and his new wife are on, thus sinking it, leaving few survivors. Jonathan drags him to the bottom of the sea with him, finally killing Dio...until he returns 100 years later, using Jonathan's corpse as a body for his severed head. Even though Dio had a hideously abusive father, his Freudian Excuse isn't nearly good enough to excuse his barbaric behaviour. To reiterate the above - he did this just because he could.
Cioccolata. OH DEAR GOD, CIOCCOLATA. For starters, his back story involves him torturing old people to death while maintaining a guise of being a good samaritan. When he starts fighting the heroes, he makes sure that he starts horribly killing the innocent people in the village just for fun. His Stand Green Day works when people are at a lower altitude than him, so what does he do? He gets on a helicopter and flies above Rome to kill as many people as possible. It says something when even the Big Bad Diavolo, a man who would kill his own daughter to protect his identity, is disgusted by him. Thankfully, Giorno proceeds to give Cioccolata the biggest and longest beatdown in the entire series, which sends him flying into a Garbage Truck with "Combustable Trash" labeled on the back.
