If you want to talk about killing, Hitler was a lilliputian compared to some of the other 20th century monsters.
Most estimate that between 11 and 14 million were liquidated during the Holocaust. Which was, no doubt, terrible. It would be like going into Belgium and killing everyone in Belgium. It is also greater than the death toll of World War I.
When discussing these stats, I prefer to count all the innocents killed by the Soviets Union. The problem was not entirely Hitler after all, he had a political party behind him that also believed in the Final Solution.
But heck, let's isolate some individuals first shall we? Mass killers are notoriously bad record keepers, but the estimate the number Stalin killed is between 20 million and 60 million people. Keep in mind some count famines and the like, others do not. I do. Solzhenitsyn's proposed number of 60 million is not improbable.
But that is Stalin alone. If you stack the bodies up, globally the number rises to about 110 million that you can pin to the USSR, China and Soviet satellite nations. That number is not counting abortions which were plentiful in the USSR.
Bringing this full circle, we have much to fear from Putin I believe. He may talk nice, but the gentlemen he associates with like Alexander Dugin tells me that there is a wider ideological agenda Putin is seeking to build.
He isn't the anti-christ, but he is a man to be feared.