Leopold gets my vote. maybe Stalin. Hilter is so palyed out though so i dont feel like talking about him. i'm a poli sci major so this is right up my alley .
None of u dudes are even close (well ok Pol Pot under Nature Broly is good) but umpteen modern regimes Africa beats the Sam Hill outta all o dat....but no one gives a shit (well fair fucks to the Yanks they tried in Somalia but realised that these folks aint for saving).
Idi Amin
Robert Mugabe
Two fine gentlemen indeed , would even have you for supper.....
I believe Stalin may have been the most ruthless, but I feel the Roman Empire did much more damage on an epic scale. You either joined the empire or were obliterated.