http://www.mangareader.net/93-35269-...apter-467.html

Tobi's plan is to "return to his former self"... or at least that's "one way of putting it".

http://www.mangareader.net/93-458-17...apter-453.html

Tobi wanted Nagato to use the real resurrection jutsu on him.

http://mangastream.com/read/naruto/94539395/3

The Impure World Resurrection Uchiha Madara initially mistakenly believed that Nagato brought him back to life.

So, Tobi is still Uchiha Madara. His plan was to have Nagato use the resurrection jutsu on him, just like the undead Madara wanted. I guess he didn't have access to his real dead corpse to resurrect himself with, or there was some other restriction. "Tobi" is Madara's soul inside someone else's body. Considering the malleability of his body I'm gonna say he is possessing the other half of Black Zetsu. Oh, and he's Obito too, still, btw.