Having fulfilled Godwin right in the title, let me just restate the question in a bit more detail.

Before the 1940s, was there a single name that was used universally throughout the Western world to signify a despot or megalomaniac tyrant, in the way Hitler is today? "Universally" means that the recipient could be safely expected to consider a comparison with said person as an insult; various leaders who are seen differently by outsiders vs. their own people (such as Vlad Tepes, if I am not mistaken) or who were hated only by some social classes or movements (e.g., Napoleon or Lenin) are thus excluded. (Note that "but Nazis still love Hitler" doesn't mean Hitler should be excluded. Literally Hitler-loving Nazis are sufficiently fringe that they would rarely ever take a Hitler comparison as a compliment, whereas I can easily imagine a Napoleon comparison being meant as a praise among liberals in the 19th century.)

Caligula? Henry VIII? Ivan the Terrible?