Obito was a weak Uchiha(what does that have to do with anything, i can also pick a weak senju......Tsunade). Not all Uchiha members are invincible(they fought senju many times and they were equals, read the manga). Sasuke is just made out to be that way because he is Kishimoto's favourite character.(he´s one of the main characters)Did you know that?(ofcourse i know and i knew that since long ago) Kishimoto loves drawing Sasuke so there's no way in hell he'll kill Sasuke off until the end of the manga.(he almost based the whole story off of sasuke, ofcourse he´s not gonna kill him!)
"Despite the time and energy Kishimoto spends drawing Sasuke, Sasuke has become his favourite character to draw."(ahhhhhh, brings back memories, i read that somewhere around 2009, i read most of the popular naruto characters, i haven´t went there for a long time, there is no reason)
^ straight from Naruto-Wiki.
I don't assume he's Madara. Whoever he is, he has got a lot of hate for Senju. He is definitely a Uchiha. Most likely Madara's younger brother, Izuna or Kagami Uchiha.(so true Izuna or Kagami, Chances of him being Kagami in my opinion is 70%, then there is also the new sasuke theory)
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As for people making comments about Madara "wanting" to lose. Tobi wants several things. His main goal is to destroy the Leaf. He also wants to control everyone and become the host of the 10-tails.
Now what do we know about Madara's past? We know for a fact that Madara did lose and die during the battle. Whoever Tobi is, he claims that he, Madara, did not actually die but was planning ahead for the future. In other words he knew he couldn't win vs. Hashirama. He just wanted his cells so once Hashirama died, he could destroy the Leaf village, his clan and even take over. If he was capable of killing Hashirama right then, he would have done so instead of "playing dead" and taking centuries to get his revenge.