In response to the other thread, I think we could use a bit more positivity. In any case, let me cast my vote for Cyrus the Great. He turned some disunited tribes into the greatest empire in the world, abolished slavery, and, best of all, his empire actually lasted, unlike, say, the Mongol Empire. Runner ups include King Mongut of Siam, Emperor Meiji, Suleiman the Magnificent, and Augustus.