Who was the cruel man in the entire world?

There have been many cruel men in the world in all ages. In the past, Pharohs (Firaun) of Egypt had been extremely cruel. Hitler was also a cruel man. Those who are responsible for killing of millions and millions of innocent humans during World Wars -I & II were also very cruel. Even now the Rulers who order killing of millions of human beings on one or the other pretext are most cruel.