There are plenty of guesses on who Tobi is. The primary one was Madara, but that is probably not the case since he was truly dead and is under Kabuto's reanimation. The point of this post is for me to give my unique opinions, ones that no one else has thought of. The first one is rather far-fetched, but it revolves around Obito. I'm pretty sure it's not him because he gave his eye to Kakashi. But what about Rin? does the manga ever make notice of her after that incident? What happened to her? Did she die on the battlefield or did she go rogue? The motive would be speculative, possibly Obito's death drove her off the deep end... Who knows? My other theory revolves around Zetsu. Whenever Tobi sustained injury (Fighting with Minato Namikaze and later, Fuu Aburame) he would break off his arm and a white liquid would pour out instead of blood. This is probably due to the Senju DNA which he was shown to have. Zetsu is probably the only person Tobi completely trusts. Since there is a black Zetsu and a White Zetsu, there could also be a third Zetsu. Any thoughts or details that I missed? Please comment.