Yea Tobi is Obito :D
Half of his body was crushed and Madara saved him.
But half of Obito's body is made of Zetsu's cells and Madara didn't take over his body he just saved him (I can say he chooses he because of hatred and etc.)
Ur Вопрос is probably why Obito is so mad?
Because Kkashi let Rin die..... xD He want to destroy the whole world because Rin died......
There is the link u can read Манга it explains everything
link There is some chapters just for Obito so u have to read other chapters to understand everything
