There are always "two's" in the system of the Mahdi. For instance Gog and Magog are two, Hazrat Mahdi (pbuh) will be against these two, insha'Allah. For instance Hazrat Mahdi (pbuh) will be against the dajjal (anti-christ) and the Sufyan. He has two opposites. He has both djin and satan enemies. Because he can both be material and soul, he might be called Dhul'Qarnayn. Because he possesses knowledge of both seen and the unseen, he can be called Qhul'Qarnayn. - Harun Yahya