The Masked Man: Planned immortality and power.
Wow... there are a lot of theories about today's chapter... I'm new here, so forgive me if do something wrong... I'd just like to get this out there, and out of mind, while getting people's thoughts on it. Unfortunately... I'm going to bet that by the time I finish posting this... several theories that are close to this will have probably popped up too...
Anyhow, my stance is that the masked man we know as Tobi is the real Madara. Naturally, the revived Madara is also real.
At some point, Madara probably split his soul (Making him weaker than he probably planned), but guessing when and how he did it is hard to guess, especially since the revived Madara has knowledge of Nagato, who is far too young to have been alive when Madara supposedly died.
"So it finally happened... It would appear that little brat Nagato managed to grow." -Madara Uchiha.
The quote above is a reference to what my revelation is... Masked Madara in order to live long enough for his goals to come to fruition, split part of his soul, and transferred it to an immortal body. Transferring his entire soul wouldn't have worked for this theory. Why? He transplanted/gave the power of the Rennegan into/to Nagato as an infant. Hence, why he has always claimed the Rennegan to be his. Assuming the plan went as planned, when Nagato grew up, and gained mastery over the Rennegan, he could than serve as the cornerstone in Madara's plan. If Masked Madara were to die and be revived by a Rennegan user, he could reunite with the rest of his soul, and regain his true power in an immortal body.
To explain further why it makes sense is because Madara could not die and use the Rennegan to revive himself. He needed someone who could use the Rennegan, other than himself. However, why Madara didn't have Nagato do this earlier though is hard to say. Perhaps Madara didn't quite trust Nagato yet, and hence sent him to capture the Nine Tails, and commit additional evil acts, making him more submissive to his will...?
On a semi-interesting/related note... Speaking of the fact that Madara Uchiha's true body has been revived, there are some interesting points... Even with it as his trump card, Kabuto's inner dialogue indicates that even with his trump card, Madara, that he could/can not guarantee Masked Madara's cooperation and willingness to bend to Kabuto's will. Kabuto's inner dialogue also names Masked Madara, Madara.
Also, Masked Madara does exhibit abilities that no normal person should have. He comments that he is now two out of six paths, if I'm correct. Assumingly than his current body is some form of his original body, and the First Hokage (I'm most iffy on this, so feel free to correct me).
Now to clear up some other things... Originally what was above was pushed down, but I decided that I just needed to get it out of the way, instead of covering some of my bases first...
Although you could say that Zetsu could have been close to the battle where Madara supposedly died, and replicated his appearance, and chakra; that simply wouldn't explain the origin of Zetsu, now would it? It also wouldn't explain why his chakra pattern doesn't freak people out anymore (Madara's chakra felt cold/evil/large, if I recall correctly). Nor would it make sense in the sense of, why wouldn't Zetsu have replicated himself as many other ninja as well before recent events? Also, the mannerisms of Black Zetsu and Masked Madara are quite different... Also, the side we always see of Madara except on one or two occasions looks nothing like Black Zetsu. The Black Zetsu entity is always on the right, and it along with White Zetsu takes orders from Masked Madara. Actually... now that I think of it, Masked Madara's left side is always obscured in darkness. Even so, that doesn't mean much as Madara has shown Kisame his entire face before, and Kisame didn't think anything was off, apparently.
Zetsu is supposedly a by product of the First Hokage's cells. At least White Zetsu is. Black Zetsu is a bit more mysterious, especially since he has no problem confronting a Kage, which puts his battle prowess likely much higher than its White counterparts. And also to clear this up, if Black Zetsu was originally whole, and Masked Madara is now his other half, than why would Black Zetsu split himself up into another being, instead of becoming whole with a new power? Nevertheless, even if part of Masked Madara is partially a Zetsu, that doesn't mean that he's actually a Zetsu, especially since all the other Zetsu take orders from him.