It's Mr T. "I pity the fool who can't pass through me!" Tbh I have know idea. I read one theory and be all, "hmp, that could be him." Then i read another and I'm like, "wait what?"
Right know I'm feeling that he's character never seen before.
i think its going to be ike a pupil of madara who wanted to continue madaras dreams onced madara lost to the first hokage and everything. or maybe not even a pupil but just a nobody who looked up to him.
It is obito's body under control of Madara's "mind/soul". That would explain why he wears a mask and only shows 1 Sharingan Eye, the body doesn't have the other Eye, Obito gave it to Kakashi.