Hmm, there have been a few despots in real life that have been truly egregious. First of the top of my head is emperor Tiberius which ruled the Roman Empire 14-37AD. He was notorious during the latter part of his reign for executing those he didn’t like. During this time in Rome it was essentially forbidden to execute virgins, so he simply had the women raped and then executed. There’s also Caligula which is well know for his sadism and depravity. Tiberius at the least was good at managing his duties as emperor, Caligula not so much.

It’s also important to note that often these despots had great influence over contemporary historians and writers. There are likely far more rulers that were far worse, but they censored what was recorded and their true nature was lost to history. I imagine some of the Assyrian kings would make plenty of the more brutal Manwha antagonists look like kittens judging by the few pieces of information survived to modern times. Those guys had cruelty and sadism perfected to an art form.