If you guys have been reading the manga carefully we've learned that
Tobi's apparently not Madara. Madara was brought back by Kabuto as blackmail. Oh joy, revel in the plot twists of the century kiddies!
We've also learned that
Everyone and their mothers thinks it's Obito Uchiha. Although it could be Madara's dead brother.
So then, who do you think he really is?