Pol Pot was truly evil but he didn’t affect as many people as Stalin, Hitler or Mao.
I think Mao was the worst.
Marx
In terms of percentages, Pol Pot is the top genocidal person in modern history, having murdered one third of his countrymen. In terms of total body count, Islam easily wins with about 400 million murdered in South Asia over five centuries. That’s 0.4 billion for clarity.