I don't know if he is the greatest warrior, but surely he is one of the greatest. I think that Garrosh is equal or close to be equal (even if he is sissy and douchebag) in terms of being warrior. Also, Thrall was very skilled warrior (yeah, now he is fully a shaman). Or maybe Muradin Bronzebeard? He is strong warrior too. Anyway, I don't think that we can call any warrior the Greatest. At least not for now.