Complete Monster/Star Wars Expanded Universe

"Cronal: Only power is real, and the only real power is the power to destroy."
 * Darth Bane in Drew Karpyshyn's Darth Bane Trilogy. When dying of poison, he forces a healer to medicate him by threatening to drop the man's young daughter into a pot of boiling water. Later, he manipulates Kaan, the leader of the Brotherhood of Darkness, into using an inherently suicidal Force technique that kills the entire group (plus the vast majority of the Jedi Order), leaving Bane the sole remaining Sith Lord. This is aside from his tendency to kill at the drop of a hat. His apprentice Darth Zannah, however, manages to actually get creepier than her master's evil, destroying a romantic rival's mind with her powers, leaving the woman basically alive but irrecoverably insane in a coma. Oh, and the tiny fragment left of her conscious mind is still somewhere in there, trapped with all her nightmares until her body dies. And showing that she's learned her lessons well, when, at a later time, Zannah has to go back to that healer to save Bane's life,
 * Cronal, Big Bad of the Star Wars Expanded Universe novel Luke Skywalker and the Shadows of Mindor, is a Nietzsche Wannabe so evil that he mentally derides Palpatine for being, in effect, too nice. His misdeeds include enslaving his own already loyal soldiers by implanting what amount to self-destruct devices in them, having captive Force-sensitives essentially lobotomized and then slaved to his will to act as extensions of himself (the real Cronal being an incredibly frail old man), attempting Grand Theft Me on Luke, and, when that fails, on Leia. His goal is galactic domination, but he edges towards Omnicidal Maniac territory when he proclaims that his rule will be "no mere second imperium, but the reign of death". He is a very effective and memorable villain, though, as his Complete Monster status makes him a great foil for Luke.


 * Another one is Onimi from the New Jedi Order. This is the dude who masterminded the most devastating war in Galactic History, who indirectly caused the deaths of trillions and the extinction of whole species, just so that he could become a god. He even tells Jaina that he's looking forward to "exterminating everyone and everything in this foul galaxy." During his Motive Rant to a captive Jaina, he does try to cast himself as a Woobie, Destroyer of Worlds, but she (rightly) just thinks he's a lunatic and is repulsed. It's made clear to the reader and both Solo twins that, by the time of the Final Battle, Onimi's motivation is For the Evulz at best.
 * To give a valid comparison, he's basically the Star Wars version of Kefka Palazzo.
 * Oh, and it's also strongly implied that his plan to descend the Galaxy into darkness had actually suceeded.
 * In a vweilu-nut shell, he's worse than Darth Sidious, Dezono Qua, Jabba the Hutt, Remart Sasyru, and Leonia Tavira combined.
 * A Complete Monster who, to some, is Evilly Affable is Ysanne Isard, Director of Imperial Intelligence and Emperor in all but name during the X Wing Series. Along with the traditional things that come from being at the head of the Empire, like oppressing nonhumans and ordering strikes against the Rebels, and what she did to the previous people in power, she ordered the creation of the Krytos Plague, which causes infected nonhumans to die horribly, and set it loose on Coruscant before the Rebels captured it. This so that the New Republic would both bankrupt itself trying to treat the infected and tear itself apart along species lines, as resentment towards immune humans rose. It might not have gotten that bad, but that was the intent. And then there's how she left Coruscant. And Lusankya. At one point, Wedge thinks to himself that Isard might not have been evil on the scale of the Emperor or Darth Vader - aside from Luke and sometimes Leia, few people in that 'verse consider Vader anything but evil even after his Redemption Equals Death - but that was small comfort to the millions who died at her hand.
 * Another one is Ta'a Chume. Let's see, she assassinates her own son, would be daughter-in-law, and her actual daughter-in-law, purely because she considers them "weak". Oh, and she orders a hit on her own Great Granddaughter because of her distaste for Jedi, sells her followers up the river, and tries to get Jaina to marry Isolder. Ugh. Not surprisingly, few tears were shed when Jacen sent her into a coma. Especially satisfying because she had been a frequent Karma Houdini until that point.
 * Moruth kriffing Doole. He keeps a harem of Rybet females he rapes, and he enslaves the children, making them package up the spice mined. Then, when they're old enough to challenge him, he kills them. Fortunately, unlike Kyp Durron from the same trilogy, he's not a Karma Houdini.
 * Pirate pilot Remart Sasyru, whose idea of fun is blasting landspeeders on the freeway. He also, on a raid, demands sex with the community Trustant's daughter in exchange for the trinkets he stole and tries to rape her when she refuses.
 * Contrasting nicely with Grand Admiral Thrawn is Joruus C'baoth, Ax Crazy clone of a Jedi Master who was a real piece of work to begin with. C'Baoth is a particularly interesting example as we get to watch him descend from an arrogant (and almost pitiable, considering his obvious mental instability) jerkass into true evil. Right around when he Mind Rapes General Covell to death is when you realise there's no going back for this corrupted asshole.