The Italian Renaissance had a pretty cutthroat political climate, but King Ferrante I of Naples carved out his own niche of crazy. Born the illegitimate son of Alfonso V of Aragon in 1423, Ferrante ("Ferdinand" in Italian) spent most of his life wrangling his Neapolitan realm into submission. The experience turned him into a real brute.
Ferrante didn't let most of his enemies go free. Instead, he killed and mummified them—keeping their preserved corpses in the castle of Castelnuovo for his own enjoyment. He loved having them close by, according to nineteenth-century historian Jacob Burckhardt, "either in well-guarded prisons, or dead and embalmed, dressed in the costume which they wore in their lifetime." A contemporary chronicler described them as "a frightful sight," having been "pickled with herbs," as a warning to future royal enemies.
How did Ferrante get so twisted? King Alfonso didn't have any legitimate male heirs of his own at the time, and he really wanted his not-so-secret love child to rule over at least part of his burgeoning empire. Thus, he gave Ferdinand the best education he could afford: tutoring by Rodrigo Borgia (later Ferrante's mortal enemy when he became a cardinal, then Pope Alexander VI). Despite his legitimization, Ferrante struggled to hold on to his territory, facing opposition from numerous popes and the French candidate to his throne, Duke Jean II of Anjou.
Needless to say, Ferrante hated Jean and his French pals, even after he beat them, so he devised his own morbid revenge. After he dominated the French in 1465, Ferrante invited a bunch of his rebellious nobles and their families over to his castle for dinner. He ostensibly was showing his benevolence, and who wouldn't want to make up over a meal? Unfortunately for his guests, Ferrante wasn't in a forgiving mood. He fed some of them to the crocodiles in his moat and threw the rest in prison—keeping some of them there for the next thirty years. The King threw another enemy out the window (the Neapolitans loved defenestration). Some of these guys probably wound up in his mummy collection.
Interestingly, Ferrante didn't just believing in mummifying his enemies. He had himself preserved as an artificial mummy after his own death in 1494. Modern scholars have autopsied his body and determined that he died of large bowel cancer.