I would choose Genghis Khan, the same preference as greaterkhaan. But my reason is slightly different.

Compare to others, Alexander, Ceasar, Wellingtong etc., the Golden Horde has a very difficult start up. While they are a warrior society, they lack the unity of other countries/cultures. Living in hash condition, with a hasher background (He was without tribe at first, after the death of his father), it's a wonder that Genghis Khan have time and mental capacity to dream of a united Mongols, then goes on to achieve that. I must note that his education would be largely about survival, not about commanding army or leading people, but he managed to learn/rediscover all the necessary skills to build/manage a huge empire.