Izuna(Madara's brother) posing as Madara......

Felt like sharing from someone's theory; It sounded posible but not sure.

Ok, why couldn't Tobi be Izuna Uchiha, I think when Madara tried to take Izuna's eyes, he defeated Madara, and possibly killed him, and he took the alias as Madara, so that people wouldn't say that "Izuna is a traitor" or some sort of thing, but his name would gain sympathy, and it worked, what did people say, "Madara is a traitor, etc", see the difference, Izuna's name gains sympathy, while Madara's name gets bad reputation,

This would explain why Tobi's sharingan is damaged, because he overused it as well, and got it damaged, but since his brother died, he had no replacement.

another proof, there were a lot of theories about rivalries, so I will be using that, Observe:

Hashirama Senju-Madara Uchiha
Hiruzen Sarotobi-Danzou
Naruto-Sasuke,

see how all the rivals are Uchiha's or sharingan weilders.

well since Hashirama and Madara are rivals.

why couldn't
Tobirama Senju and Izuna Uchiha be rivals.
and
I think that Izuna used his rivals traits, as a symbol of their rivalry, and also to avoid possible suspicion.

also, I think Izuna is alive, because, he is a key character, and doesn't seem like would die that easily.

The databook does state that he died, but, Itachi was also believed to assassinate the whole clan, by himself,
where as two things:
Leaf ordered him to do so.
Madara helped him.

were not revealed, so with the pen in hand, Mr.Kishimoto, can do anything in Naruto,

so, what do you think of this "sort of theory".