It's his bro and here is proof! http://naruto.wikia.com/wiki/Izuna_Uchiha see the little second picture on the left

finally someone posts a reference I TOLD YOU GUYS IT WAS HIS BRO

i dont beilive anything from a wiki page

also thats just him in his casket already mentioned in the thread its from a flash back not a summon

Well Izuno is the only Uchiha that is blindfolded.Sage of Six Path was never blindfolded and no one took his eyes out yet.

Don't think it is the Sage of six paths, I think it is the first hokage or his brother.

None of the Hokages 1-4 can be brought back, as they are sealed in anothher dimension, their souls are not in the "pure world" aka afterlife, they are in Death God's stomach with the sealing technique the 3rd used on the 1st and 2nd when Orotchimaru brought them back with Edo Tensei and the 1st's, 2nd's and 3rd's souls were sealed. The 4th's soul was sealed when he used the same technique to seal Nine-Tails inside Naruto. Kabuto explained all this, don't you remember?
Now for his brother, they were equals YEARS AGO, before Madara took the Eternal Mangekyou Sharingan, Rinenngan, the 1st's cells, Bijuus 1-7, Gedo Mazu, and more simply after training and practicing new jutsus after more than 50 years. Of course, he said before that now he is a mere shell of what he was before, but Kabuto said that when he revives someone, the revived one is exactly how he was when he died, and Izuna died after Madara took his eyes in the battlefield, so he would be useless, as he would be without eyes. :P

that brings up the question of who the third summon for orochimaru vs 3rd hokage was. it was implied it was the fourth but never specifically mentioned.

IMO it was the fourth but its just a plot hole which tends to happen with long running series

Kabuto said that it was the 4th, and Orotchimaru failed because his soul wasn't with the dead ones, like I said before.

look guys all i know is that the Rikkudo Sennin/ Sage of sixth path is way more intimidating than Madara's brother.....just think about it, its obvious thatNaruto, Bee and Sasuke (in the end) are gonna join forces....it has to be some god-like enemy...im sure Sasuke alone can beat..Madara's bro psshaww!

LMAO Rikudo senin? you guys are funny seriously how can kabuto find the god of this world ? and if ever he find him, nobody will be able to summon him, too much power, and btw i think its madara in the box cause if you listen, at the meet kabuto say " hello Tobi, oh its true you get called Madara those days" , and we know that madara is the best of the uchiha clan, "tobi" can't beat him so he was forced to accept, and more kabuto say "i know your little secret' something like that, then he say that he tell it to nobody, so that's why tobi was unable to refuse. and if he attacked him, he will lose against kabuto cause he just can't beat madara. and why tobi don't have the mangekyo of madara? why tobi have only one sharingan ? and from when madara have teleportation powers? only shisui was having this power, and denzo steal one sharingan to shisui so i think that tobi = shisui, and the guy in the box is madara :p there is more proves of this than tobi is madara or someone else -.-