Before Hitler, who was the gold standard for pure evil? Like, when people were referring to the epitome of a horrible person, who was the default, “Yeah, that guy’s going to be the next ____” before WWII?
/u/kratistos assembled a list of the groups and individuals likely to take that title in this thread, though some of these are specific to regions or certain time periods. You can also check out some other answers to the question via the FAQ.