Pol Pot gets my vote...but if we want to dip back into the early 16th century, there was one bad mofo Aztec named Tlacaellel who would sacrifice thousands of human beings each week. There are actual records that he had over 80,000 sacrificed to the Aztecan almighty sun & war god Huitzilopochtli in a period of just 72 hours. That by all means is impressive. He lived to be 98 and never gave up ripping the hearts out of the chests of his fellow Aztecs nor the neighboring tribes all the way through his old age.
So....just to add one, Tlacaellel. Montezuma II was a nasty mother too, but that would require a lot more story telling. Tlacaellel just liked mass sacrifices.
