Princess Chalchiunenetzin from Gary Jennings's novel Aztec.
The fifteen-year-old bride of King Nezahualpili of Texcoco, the daughter of the Aztecs' King Ahuizotl. Convincing her husband that she was merely an innocent young girl, she seduced young palace servants and coerced them into coming back again and again against their will -- if she told her husband that they had raped her, say, they'd die. When she tired of them, she tossed them aside and had them murdered. She went through several men like this -- and all the while, out of a perverse desire to have someone watch her while she did it, forced the novel's protagonist, Tlilectic-Mixtli, to witness it against his will and take notes for her to peruse at her leisure. After getting tired of men, she decides to "sample" a young woman just to see what it's like, whom she forces into bed against her will with the threat that she'll have the woman's husband killed if she doesn't; the woman commits suicide out of shame and self-loathing shortly after.
She has a disturbing desire to flaunt all of this under her husband's nose, so she orders her servants to take the bodies, boil them down to the bones, and put the skulls into statues, which she then has placed in her quarters. She tells her husbands that the statues are sacred representations of Aztec gods she brought with her to remind her of home.
In the end, when her vile deeds are uncovered, she is sentenced to die in a truly horrible way. Locked in a huge maze of thorns, she runs desperately along the passageways, her skin torn all over, until she comes to the center, where she finds the corpse of her last lover, now being devoured by flies and maggots, and loses her mind. Chalchiunenetzin dies from starvation and exposure.
And even so her evil lives on as her unwilling accomplices are punished. Since Mixtli had been a friend of Nezahualpili, he is merely banished from Texcoco. The other servants, on the other hand, are not so lucky. All of them -- her messengers, those who disposed of the bodies, each one -- is sentenced to die by the garrotte, which is even worse than sacrifice because it means their souls cannot enter paradise after a bloodless death. Mixtli's closest friends Tlachtli and Chimali -- who were lovers -- were the ones who made her statues, but Tlachtli takes the fall for Chimali and dies. Chimali swears eternal revenge against Mixtli for getting them mixed up in this (he got them the job at the palace), which results in the castration of Mixtli's boyservant immediately after the trial, and ultimately ends with the death of Mixtli's wife years later.
King Ahuizotl is outraged that his daughter has been executed and looks to punish Nezahualpili. So he declares war against the nation of Texcalla and, using his seniority among the tribal chiefs of Mexico, orders Nezahualpili to send his best warriors against the enemy while he sends only a few old and infirm soldiers. In the end, Texcoco is decimated while Ahuzotl's Tenochtitlan suffers minimal casualities.
Now that's evil.
