Tobi identity theory-obito :(
Shit ton of text incoming:
I honestly wish for this theory to not be true. However from what i can perceive it is in the realm of possibility.
Tobi has a possible chance of being obito, though i find that chance very low i believe i have came up with a theory that is possible(even though i don't choose to believe it) All i am saying is that it's possible for this theory(as many theories are to be true)
Obito clearly gets his body crushed by a rock, impossible to survive from. IMPOSSIBLE TO SURVIVE FROM.
Now on to Madara, we know that Madara survived his fight with Hashirama. He lived for an unknown amount of time and then was able to obtain the rinnegan. One of the rinnegans abilities is to bring people back from the dead. As displayed by Nagato reviving paths of pain to perfectly regenerated bodies and reviving the recently deceased people of konoha.
I believe that it is possible for Madara to have lived until(or awhile after) obitos death. After Obito's death it is possible for Madara to have revived obito noticing the potential he has(reviving him this way he was able to revive his body in perfect condition including his sharingan).
After Madara revives obito he uses his sharingan in order to manipulate his mind turning him against konoha and turns him into his pawn. Obito grows and gains the ability to use his sharing.
He trains with Madara for awhile until Madara dies, and madara tells him everything he needs to know about his plan.As an Uchiha Obito is able to use the sharingan much more efficiently than Kakashi and is able to use space time techniques with his eye on a whole other level and is actual able to teleport large objects multiple times to different dimensions, and can phase through objects. During training he wasn't able to phase his entire being on the first try and lost parts of his body to the technique. the parts lost were replaced by the stuff zetzus are made out of.
Anything previously done before obito became tobi would have been done by madara, explaining longer hair in some circumstances.
After training with madara, it explains how he was able to gain the ability to control the ninetails and how he was able to become strong enough to fight near the fourth hokages level.
This theory would also assume that tobi did not give Nagato the rinnegan since madara would have had them in order to revive obito. in this situation i would assume that Madara gave Nagato the tools to obtain the rinnegan without negate knowing and tobi takes credit as he does for many other things madara did.(if you want a theory where nagato clearly gets the rinnegan from madara/tobi then madara could have just used zetsu glue to repair obito(though i find that very unlikely because that would be unable to reform his eye))
Tobi has marks underneath his marks looks like signs of old age perhaps, however for this theory i would say its from years of battle and overuse of his sharingan.
However i think this theory is complete bullshit(not in theory, just i would hate for Madara to have lived for so long and obito to have such a large change in personality.)
Alternate theories just said really fast not involving Obito:
I prefer a theory that would say Tobi is an advanced zestu clone(Black white mix) with Madaras chakra in him, which in naruto apparently represents part of the soul as shown by narutos parents and orochimaru. So part of madders soul would be in tobi. i would think something like that would be much more possible. I would even think izuna being him would be much more possible(though his age he would have to be makes me think not.)
Also yes i know there is an "official tobi id thread" however that thread is 400 pages long and hardly anyone wants to read through 400 pages.
One more thing, text edit was doing dumb things such as turning words to tobi into obi and obito into obit and sharingan into sharing and other stupid things so please excuse some typos.