Adam Smith and David Ricardo: I am a bit suprised neither of these men have been mentioned; though admittedly I do not know much about their personal lives. Nontheless:
I enjoy living a comfortable life (I am not be able to fathom a life where I could not access internet forum discussions online!). More than that I enjoy having a standard of living that is approximately 1000x greater (materially speaking) than what most of human history has enjoyed. The astronomical increase in wealth, generated by the ideas of specialization of labor and comparative advantage laid the foundation for liberal human rights and advanced technology; to attempt to list everything else would be an exercise in futility.
My apologia for these men certainly does not do them justice. However, I thought someone should at least mention them (where are the economics students?). Also maybe I am confusing 'favourite historical personality' with 'most significant impact'. Though I would certainly want to meet these men who formulated such groundbreaking ideas.
I realize that the above post is not really about a 'favorite personality'. In that case, my favorite historical personality would be Socrates: "I am the wisest man alive, for I know one thing, and that is that I know nothing." His quest for knowledge is a much more lasting and pertinent achievement to me than forging an empire upon heaps of human bodies.
Which leads me to the point, why is Hitler such a 'favorite'? He was not the first person to exploit fears and certainly not the first to kill millions (though he may have overseen the first systematic extermination of a specific race)? Psychologically, he seems nothing more to me than an obsessive, egotistical politician who found an easy target in the Jewish for a propaganda campaign.
A second favorite personality would be Shakespeare. His insights are acute and meanings so cleverly hidden. A quote for this thread might be, "When that the poor have cried, Caesar hath wept: Ambition should be made of sterner stuff."