It's time for another awesome theory from ELITE SENSEI MASASHI. This time it's about Madara, and the truth behind that mask.
Who is Tobi? He claims to be Madara, yet most other characters find that impossible since he supposedly died many years ago. However, he claims to have survived through his powerful chakra and is still suffering from a wounds inflicted upon him by Shodai. It seems unlikely that a prodigious ninja like Shodai would be unable to determine if someone was alive or dead, or that a ninja village would so carelessly leave the carcass of a powerful ninja from their village just lying somewhere.
Then how did Madara get away without anyone knowing, and people believing he was dead?
He didn't, he died at the Final Valley.
But in death, he became a symbol of rebellion for the Uchiha who'd become aware of what Konoha and the Senju had reduced the clan into becoming. From there on those who rebelled would take on the name of "Madara" and carry out their plan of Uchiha supremacy for the true members of the clan and to return them to their origins.
In speaking to Sasuke, Tobi mentions after his(Madara's) death, other Uchiha became aware and rebelled, and in that very same scene we see them standing before a pillar that says “Madara.”
But how does he know so much about the Uchiha, and Madara's past specifically? Information that has been passed down through the generations among the various Uchiha who've taken up the name of "Madara.” Itachi himself was able to show Sasuke the history of the Uchiha through, displaying a piece of "Madara's" past with his brother, and even that fateful night when Madara took his own brothers eyes to acquire the power of the Eternal Mangekyou Sharingan. The past is no secret, and nothing Madara said was so personal as to prove whom he claims to be, rather they are general observations that anyone could have made.
It is true that when talking about Izuna he seems to show some discomfort, that doesn't mean that he's connected directly to Izuna. Instead it's possibly a ruse to misdirect anyone listening to his story, or he may be empathizing with the actual Madara. There are other reasons to suspect the current person posing as Madara, is not actually Madara. He continues to wear a mask, despite telling everyone that he is actually Madara. It's unnecessary to hide his identity from anyone, yet he continues to do so, and any time we get to a point where he's about to take his mask off there is an interruption. It implies that his appearance is a plot device, we're not meant to see what he looks like because it will end up being a revelation, the most obvious is that he is not Uchiha Madara. It's also possible that he's horrible scarred, or deformed, but that's unlikely to be the case as we know Madara is injured and stringing us along for this amount of time over simple scars and disfigurement is overkill. No, whatever is behind that mask is important.
We also have to ask ourselves; "What is so important about the body that Kabuto has?" Edo Tensei is a technique the resurrects the spirit of the dead, and whomever Kabuto resurrected, it seemed that it was direly important to Madara that he not tell anyone about it. Even to the point of offering Sasuke up as a sacrifice. Others have speculated that it was Rikudo, or even Izuna, but these guesses are all clearly wrong as it wouldn't hinder Madara in the least for people to know about Kabuto bringing these souls back. But if it was Madara that Kabuto was able to raise, then there would be a very good reason to keep this swept under the rug if you're going around claiming to be him. It would also explain why Kabuto felt that this would be a good bargaining chip to use against Tobi. All in all, though this man may claim to be "Madara,” he is in fact merely one in a line of succession to carry the title of Madara. Possibly even grooming Sasuke to one day take over the title and carry on the legacy, to bring the Uchiha to supremacy.
Plus Tobi is clearly Obito!