I think Tobi is the Senju Clan Ancestor.
Why I believe Tobi is the Senju Clan Ancestor (along with a few more theories);
- Tobi told the story of the Sage's sons from a neutral point of view, but he had nothing but bad things to say about the Uchiha Ancestor. Think about it like this, the story would've been told similarly if coming from the Senju ancestor.
Tobi basically explained that for one reason or another, So6P chose his younger son(Senju) instead of his older son to carry out his dreams of peace, which seems unusual in itself. He then went on to explain that envy caused the Uchiha Ancestor to attack the Senju ancestor.
Heavy speculation, but is it possible that the Senju Clan Ancestor one way or another manipulated the Sage into choosing him, and the Uchiha Ancestor saw through it(possibly with his special eyes?) and attacked the Senju Son due to his wrong doing? Just some food for thought.
- It would explain how Tobi has Senju and Uchiha DNA, making him able to use Izanagi, because the Sharingan could count as Uchiha DNA. Also the fact that Tobi could use "Perfect" Izanagi (Like a pro, I might add), and Danzo couldn't, that alone tells me that Tobi has genes or experience that help him use the technique better.
- Tobi and the Senju clan ancestor have strikingly similar appearances/sillohuettes (Similar hair, identical eyebrows, identical placement of forhead apparel, nearly identical eye and nose shape, with just a few more wrinkles on Tobi).
- This would also explain the mask, because maybe there's a chance that people would recognize him possibly? It's seems unlikey Kishi showed us the appearance of the two ancestors for nothing, so their appearance might be vital in one way or another.
- This would explain how Tobi lived to such a rediculous age. Remember it was the younger son whom inherited the Sage's body, thus causing Senju's to have incredible longevity. Something that Tobi most definately has. This is also one of the few theories (I can think of) that explain Tobi's rediculous age.
- This would also explain how Tobi has a lot of rather apocraphal information that would otherwise be too esoteric for anyone else to know anything about.
- This could explain the statement in which Tobi refers to himself as "A shell of [his] former self." Since we know for a fact that the two Sons battled (Well according to Tobi anyway, though this actually seems true), it's possible the battle left him so heavily damaged that he became weakened. It would make sense that his own brother could do that level of damage to him.
- Also, If Tobi was the Senju Clan Ancestor, it would be a hell of a twist and change of allegiance. And we know how much Kishi likes those (Itachi, Sasuke, Nagato, Gaara, Konan, Zabuza, ect).
ISSUES WITH THIS THEORY,
Not many, but the biggest one is the question as to why the Senju Ancestor would have the motivation to do everything Tobi has done/claims he wants to do. My response to this is that, like stated above, if he truly is evil enough to warrant his older brother attacking him, maybe he's been evil all along, and has been planning the events that are taking place for some time.
UCHIHA ANCESTOR/SAGE'S ELDER SON THEORY
- There isn't much evidence supporting this son as Tobi's identity. Infact, the only real support for this claim is that the Elder Son would likely have a motive for the actions Tobi has done, at least according to Tobi's description of him. That as well as the Elder son is one of the few people who would has access to the information Tobi has.
- Also this would explain Tobi's "Shell of my former self" quote, because at the time when that was said, he had no rinnegan. Something the Elder bro was said to have, or at least some form of it.
- This might also explain why Tobi believes Nagato's rinnegan belongs to him, though he also may have been speaking from Madara's point of view at the time, a habit he kept up until quite recently. Though it could be argued that since Konan was near death, he is less likely to lie. To anyone who thinks that, keep in mind we are talking about Tobi here.
- There's a mild resemblence, (Tobi's hair during flashbacks).
MADARA CLONE/CREATION/Zetsu-type thing
- The strongest evidence for this theory remains the same as always. Tobi himself has stated, even in private, that he has the power of Uchiha Madara. He also told Konan that he was Uchiha Madara with the powers of Hashirama Senju when he knew she was as good as dead. Of course very little of what Tobi says can be confirmed as true, so this isn't really hard evidence. Though
this leads to the next piece of evidence.
- Multible important and wise characters, like Minato and Jiraiya believed Madara was somehow involved with the Akatsuki, even though he hadn't even met Tobi face to face. He simply figured that out on his own. This alone gives some credibility to the fact that he actually is Madara, or his creation or clone of some sort. There must be some reason behind these feelings or they wouldn't have been noted (hopefully).
- Muu's splitting ability was introduced just a chapter or so before Madara was shown to be resurrected with Edo Tensei. This couldd be foreshadowing.
Another thought on the “split theory” is that Edo Madara thought Nagato revived him before he realized what is going on. Tobi mentioned wanting Nagato to do just that for himself. Again, he was likely speaking from Madara's point of view, but still the fact that he even knew Madara's plans concerning Rinne Tensei simply proves that he was involved with Madara closely.
Problems with this theory:
- We've already seen the majority of Tobi's face, and there dosesn't seem to have any hideous deformity indicating him being a Zetsu clone, or even a resemblance to Madara or any other tell tale sign of this scenario. Not to say this theory is out the window or anything, but that is worth noting.
- Edo Madara seems to believe what Kabuto told him through Muu, which is basically that Tobi isn't entirely trustworthy. It seems strange that Madara wouldn't trust his own creation.
Obito
- This would explain virtually nothing and leave more questions than answers.
- Anyone who honestly thinks this is mentally retarded. That being said, if this was the case, Kishi isn't much better.