Tobi is Madaras body!
Let me explain.
The now summoned Madara is the real Madara, if you will. Edo tensei does one thing: It binds a soul from the afterlife to a sacrificed body. So Madaras soul is now attached to a sacrificed body.
As soon as he is summoned he refers to Nagato. He expected to be summoned by Nagato! But not by Edo tensei. He expected to be summned by Nagatos Gedo Rinne Tensei, so he must have known Nagato in the not too distant past, quite some time after he fought Hashirama. Madaras plan was for his soul to be brought back to his own body by Rinne Tensei, but Nagato delayed that plan and now Madara is in the wrong body ^^
After Nagato used Rinne tensei, Tobi was angry, because that technique was supposed to be used for him. I still dont know who that guy is, but i am sure that Madaras soul was supposed to be summoned into Tobi. He is probably Madaras body being kept alive by Zetsu and Hashiramas cells.