My initial reaction, and the reason I started the thread, was because I was leaning toward Pacifist thought. Now, the fact that we are in the current world situation we are leads me to believe that maybe my choices aren't really as significant as I thought. But even so, I can dream about it, can't I?
I thought that Einstein was a given for his scientific thought, theories, work and accomplishments. I thought that put him into the top echelon right there, but the thing which pushed him up another level was that he basically did everything he did, with only a modicum of pride, and then he renounced it when he saw it being used for destruction. He was not only the greatest scientific mind of the century, but the one, who by realizing what he had wrought, felt the desire to basically renounce any and all of it which was used for violence and destruction. I admire him immensely.
Then, I thought of another non-violent person. In the U.S., we had Martin Luther King, and I don't want to denigrate any of his immense legacy which still affects our society, but before King, Gandhi used non-violence, and when he was finished with his stance, billions of people were freer than they had been previously. Now, I don't mean to attack the British Empire. I'll attack any attempts my own wonderful country does which ever seem to be imperialist, but the Empire was well-represented all over the place, and this stubborn, skinny guy, who refused to eat, basically brought down an Empire. Of course, it was a long journey, and WWII had a deep effect on everybody, but Gandhi was able to accomplish so much while
seemingly doing so little.
As far as dictators go, Hitler obviously affected millions of people and will continue to do so. However, if you want to go with the most current numbers we have, Hitler, Stalin and Mao are in a race to become the greatest mass murderer of the 20th century. They are all responsible for staggering numbers of deaths in the millions. The thing is that Hitler's murders were done more out in the open even if people say that they had no idea at the time. It's more difficult to determine the millions of dissidents and undesirables who were killed in the Soviet Union and China during the 20th Century. Therefore, even if Hitler is the Poster Child for Insane Megalomaniac Dictator, he may actually end up in third place, compared to the mysterious, unknown atrocities committed by the policies of Stalin and Mao.

I'm disturbed these guys are smiling, and I hope you are too.