I know some people who wouldn't even know who Chairman Mao or Stalin are, however so many people today consider hitler to be the absolute worst human being in existence simply because of how many people he killed. I'm sure this question has probably been asked before on this sub but I have never seen it.
This is an extremely common question and a search for "hitler stalin mao" will bring up many others. Here's an answer I wrote a month ago: https://www.reddit.com/r/AskHistorians/comments/70ox7m/why_isnt_stalin_viewed_the_same_way_as_hitler/dn4vf53
ETA: Also, where does one find these alleged people who have never heard of Stalin and Mao? I have heard of them a million times, but I don't think I've ever met one.