Hitler is often used in comparison or in allusion to the worst human being ever. For example "They're worse than Hitler!" Or the line from The Office "if I was in a room with Hitler and Toby and had a gun with 2 bullets, I'd shoot Toby twice."
Was there any historical figure before Hitler that was used in this regard in normal conversation? English speaking or not.
This question has been answered multiple times in various forms:
https://www.reddit.com/r/AskHistorians/comments/5x8vs9/before_hitler_who_epitomized_evil_in_popular/
More can always be said, but this older answer should be of interest