Charles VI of France, perhaps. He had some kind of issue which caused him to, among other things, periodically believe he was made of glass.
Caligula clearly had serious mental issues!
I've heard that's up for dispute, considering the historians who wrote of him were his enemies.
Ivan the Terrible ranks pretty highly for me, anyone who can set up secret police with religious overtones and all the authority of a state-run mafia, and even partake in their slaughter is pretty damn out there.
I have also heard that mercury poisoning may have caused some issues with him.Well, Ivan has the rare (for monarchs) excuse of having been psychologically abused and beaten his entire childhood, so there's that. Even so, there was still some humanity to him until the death of his wife, as I understand it.
I've heard that's up for dispute, considering the historians who wrote of him were his enemies.
Ivan the Terrible ranks pretty highly for me, anyone who can set up secret police with religious overtones and all the authority of a state-run mafia, and even partake in their slaughter is pretty damn out there.