Gilles de Rais
Gilles de Rais was, for a time, a dude. He was born into nobility as a member of the House of Montmorency-Laval, and despite being orphaned, still managed to marry up, wedding Catherine de Thouars of Brittany. He eventually became a knight and a lord, and he fought for French independence alongside one of the country's greatest heroes, Joan of Arc. He also went broke trying to stage grand theatrical productions and he was also maybe a total fucking monster.
By the mid 1430s, de Rais had had enough of war, retreating to his home to build the Chapel of the Holy Innocents, the name a reference to a story from the Gospel of Matthew, in which King Herod of Judea orders the murder of all males under the age of two in an effort to kill the newly born king of the Jews, aka Jesus. Why would de Rais name his church after such an awful thing? Glad you asked! There are two theories: 1) it was a reference to the still-raging Hundred Years War between France and England, and the generations of Frogs who'd known nothing but war and death, or 2) he was history's first known serial killer, having murdered perhaps hundreds of children, many in an effort to raise a demon named Barron who was a practitioner of the art of alchemy.
Despite having been one of his nation's most decorated soldiers and wealthiest men, de Rais really needed the help of someone like Barron, because he was dead-ass broke, having spent much of his fortune putting on theatrical re-enactments of some of his own military exploits, lavish productions like Le Mystère du Siège d'Orléans, a sprawling epic with a cast of hundreds, and more than 20,000 lines of dialogue--bear in mind, this was meant for the stage.
To support his theater habit, de Rais sold off numerous real estate holdings, finally raising the curtain on his grandest folly on May 8, 1435, with de Rais providing food and drink for the audience. My guy was burning through so much cash that his family sought help from the king, who forbade de Rais to sell any more property, forbade his own subjects to do business with de Rais, and forbade the people who'd bought de Rais' castles from selling them.
In 1440, de Rais got into an argument with a priest and settled the dispute by kidnapping the man. This of course caught the attention of local authorities, who launched an investigation, which in turn led to the suspicion that de Rais had been murdering--and possibly raping--scores of children, mostly boys.
On September 15, 1440, de Rais was arrested, a trial ensued and de Rais finally confessed to his crimes on October 25. At 11am the following morning, de Rais was led to the gallows, strung up by his neck and hanged. Though crimes of his magnitude typically called for the executed to then be burned, de Rais was, at his request, taken away and given a proper burial.
Gille de Rais' guilt went unchallenged for centuries and he became something of a bogeyman of French folklore, though in recent years there's been an effort to rehabilitate his reputation, with his defenders pointing to a paucity of physical evidence, a confession they insist was induced by torture, some accusers and prosecutors with questionable motives, and the fact that authorities allowed him to be buried, rather than burned.
Was he guilty? Who knows? By the guy was definitely a little nuts.