What do you guys consider greatness to be? Who, throughout history represented this meaning? Which men were truly great? (by men, I mean human; male or female )

I'm not exactly sure what greatness is. Its one of the questions that has been bugging me for quite sometime: what does it mean to be great? is it to simply accept who you are and realize your limits...or is it to never accept anything, break all the rules to pursue your goals?

I'm in the process of writing/researching greatness and great people and the qualities they all shared. (This is not for school or anything, its just for me).

Some names I'll throw out: Pope John Paul II, Julius Caesar, Alexander the Great, Hannibal, Dostoevsky, Hitler (!!) - could he be considered great??