Complete Monster/The Dresden Files

Harry Dresden has had to face some pretty nasty villains over his long career. The worst of the lot include:


 * Heinrich Kemmler. Dear Lord, Heinrich Kemmler. The man started World War I, regularly consumed the spirits of the dead for power, attempted to reanimate the contents of mass graves outside pretty much every concentration camp in Europe, and developed a ritual for consuming the life force and spirits of a city to turn himself into a dark God, and these are considered the least of his crimes. Even Bob, a completely amoral spirit of intellect, calls Kemmler a monster and his brand of necromancy sick and twisted.
 * Considering that Kemmler's namesake is a necromancer in the Warhammer Fantasy Battle Fantasy universe, this should surprise no one.
 * Nicodemus Archleone is the leader of the Order of the Blackened Denarius, a group of mortals who each received one of the silver coins given to Judas for betraying Jesus, which each contain a Fallen angel. Generally, once someone makes skin contact with the coin, the mortal will become possessed and then either become subservient or deeply corrupted by the Fallen in their coin. Nicodemus, however, is so evil that he has voluntarily entered into an equal partnership with his Fallen, Anduriel. In his first appearance, Nicodemus is attempting to use the Shroud of Turin to create a powerful plague to unleash upon the world and wipe out millions. He did something similar in history with the Black Death. When Shiro, a Knight of the Cross, exchanges himself for Harry Dresden's safety, Nicodemus has the old man tortured to death, and mutilates him so badly that he's unrecognizable when next seen. Though defeated in his first appearance, Nicodemus gets the last laugh by throwing one of his silver coins in front of a toddler, forcing Harry to grab the coin and become possessed by one of the Fallen in order to save the boy from being possessed. His second appearance has him kidnapping Ivy, a little girl who is the living repository for all recorded information, and torturing her so he can force her to become a Denarian and gain all of her knowledge.
 * Lord Raith, King of the White Court and the head of House Raith, manages to stand out amongst his peers as one of the cruelest White Court vampires. While all the Houses of the White Court feed off of the emotions of their victims to maintain their power, House Raith feeds off of lust, which they feast on through sexual intercourse. In order to maintain his absolute control over his household, Lord Raith raped and fed off his daughters to make them his slaves and murdered his sons to prevent them from becoming threats. This behavior stopped when Raith killed Harry's mother, who used her death curse to ensure that Raith could no longer feed and gain power. This forced Raith to limit his magic usage and act through mortal intermediaries. When a former employee of his, Arturo, begins to work independently as head of his own porno studio, Raith arranges the murder of several of Arturo’s workers to force Arturo to work for Raith again. Yet these plans take a backseat once he discovers that Harry is the son of the woman who cursed him and that Harry's death would enable him to feed again and regain his former glory. By the end of the novel, Raith has attempted to kill his son Thomas, plans on keeping Harry's Love Interest, Murphy, as a Sex Slave, and intends to rape Inari, his youngest daughter. Not only would this put Inari under his control, but, because White Court vampires start off as mortals and don’t turn into vampires so long as they lose their virginity to someone they love, this would doom her to a life as Horror Hunger ridden, White Court succubus like the rest of his children.
 * Capiocorpus, also known as the Corpsetaker, is one of the few surviving students of Heinrich Kemmler, one of the most powerful and evil necromancers ever- and she certainly learned her lessons well. The Corpsetaker defines herself as being the most sadistic and cruel of the necromancers in series in her pursuit of the Darkhollow, which would require her to consume the souls of thousands of innocent people. Corpsetaker regularly performs body theft to prolong her life, reveling in the agony of her victims as she steals their bodies and lives from them. After her physical form is destroyed, she shows a penchant for enslaving other ghosts and torturing those in her way with nothing but sadistic glee.
 * One of the most ancient, powerful and evil vampires in existence, Kukulcan, the Red King, is the founder of the Red Court, and the creator of a system of slavery and oppression that spans thousands of years. The Red King presides over a court that enslaves mortals in addiction to the vampires, as cannon fodder, slaves and food, with a special emphasis placed on feeding upon children, as well as human sacrifice to his own glory. When war begins between the wizard White Council and the Red Court, the Red King shows that he had already been prepared for a protracted and brutal war by launching violent attacks, including poison gas, with civilians being collateral damage at best, and food for his soldiers at worst. Playing the part of a blood-addicted junkie, the Red King manipulates his courtiers, pitting them against his enemies and one another and shows no compunction in sending his own daughter to her death when she opposes him. The misery of the Red King's actions makes South America into a living hell for civilians and those who dare to oppose the vampires, and is so horrible a formerly loyal servant is driven to Knight Templar levels to destroy the Red Court at any cost. Fittingly, the Red King is brought down by a sacrificial spell he intended for Harry Dresden's entire family line. One he was going to initiate by sacrificing Harry's young daughter personally on the altar.
 * And then there's the Skinwalker and what it did to Thomas: namely, kidnapping him, torturing him by flaying him alive until his vampiric Healing Factor is about to give out, then giving him a random, innocent woman. Since by this point, he'd have completely lost control of his Hunger, he'd wind up raping them to death. And the Shagnasty did it again. And again. Probably the most disgustingly cruel thing you could possibly do to someone trying to be a Friendly Neighborhood Vampire.