If you are thinking along the lines of historical significance, probably Marco Polo. His book led to exploration, the colonization of America and other continents, and so on. He practically started the history of the modern world. Also Jesus. His religion causes a lot of wars and was one of the factors for exploration.
Along the lines of moral impact, I would say maybe Lincoln, mainly because I could not think of anybody else. Yet, he was a man who kept cool under pressure and strove to unite the nation. And Jesus, because, you know, dying for our sins and all that.
As for true bad-assery as this thread seems to suggest, I say Theodore "I will fuck you up" Roosevelt. He is a man's man. He got shot in the chest and then gave an hour and a half speech while bleeding in front of thousands of people. He went blind in one eye after getting hit in the head by a world championship boxer he was fighting for FUN. MAN'S MAN!