Naruto Thread (Spoilers For Sure)

Tobi could be Madara himself. Maybe Madara split a part of his soul into Tobi's body so that he could use it while his real body died. Another theory would be that Tobi's actually a Zetsu clone that combined his own powers with Hashirama's cells to make a strong enough body to use as a substitute until Madara could use his original body.