system
A chat on subreddit /r/NoStupidQuestions
human
There were plenty of shitty tyrant rulers.  Nero… no one liked Nero.  But he didn’t have the body count and committed suicide once everyone turned on him.  Genghis Kahn was awful to everyone who resisted being conquered, but there was no racist slant to it: you were just in the way is all, and it was all good if you just surrendered from the get-go.  Vlad Dracul allegedly did some really sick shit, but he kept the Turks away and apparently the locals liked him all right.

It’s hard to find someone earlier than that who had the mix of the hatred/evil and the ability to express it on the scale Hitler did.
gpt
There's actually much dispute about how bad Nero was. Like a few others, he was mostly despised by the aristocracy who ended up writing the history annuls so the source material is quite biased.