i think tobi is obito ( 80%) and madara brothers (20%).... this is becoz there are so many facts that leads to obito is tobi...
1) kakashi said that his eyes and tobi are related and its look like from one person (obito) and tobi said the eyes was taken at the bridge where tobi was burried during the war. and like other said that obito was considered dead but no one ever try to confirm it, not even itachi. and its hard to find any others reasons why that tobi eyes and kakshi are related except that is from obito.
2) tobi didnt take that eyes from obito becoz this eyes never been replaced by tobi for so long( its been using for ages) , while the others eyes has been change from sharingan to rinnegan. this show that the rinnegan eyes is replaceable but not the right sharingan eyes because its originals.
3) obito isn not deads but been saved by either his eyes jutsu ( teleport his body into other demension) or saved by zetsu ( i believed this is the firts meeting between zetsu and obito) . Zetsu maybe give him a new grown up body or 1st hokage cells like danzou.
the proof is that tobi has lost his arm a few time and get bur by sasuk amaterasu, but he come back normal each times.
4) tobi surely reconize kakashi even they first meet during the search party of sasuke (5 kages summit)
5) Tobi realy hate and mad about kakashi, he mad becoz kakashi always says something bad ( kakashi always says something bad to obito when they kids) . And kakshi didnt kept his promise to take care of rin.
6) tobi is familiars with the konoha - its shown when tobi attacked the 4th hokages when naruto gets births. so its needs someone that in that era not from the old days to get familiars with the villages, and i guess it obito.
7) maybe there is a fact that during the tobi attacks konoha using kurama, kakashi and others is still young ( is just a few years after obito burried at the bridge) , this fact seems confiusing but i believe that maybe obito gets a grown up body and he use it to attacks konoha.
8) this is why kishi never reveil the true face of tobi...
1 It still could just b Obitos eye. And noone went to confirm his death because everyone assumes that when your smashed by Xthousands of pounds of rocks you are dead. And Obito was a low Uchiha who was not expected of much so noone really cared either way.
2 This point doesnt make much sense because Tobi character appeared after Obitos death meaning AGAIN it could still JUST be Obitos eye.
3 Zetsu is more likely to use/help someone who already has serious power/jutsu. Again NOT Obito.
4 Every1 recognizes Kakashi including ninja of foriegn nations and especially ninja of Konoha.
5 Plausible for the character but not probable 2 want 2 kill Kakashi and take over the world.
6 If you believe this then any Uchiha or anyone for that matter could plausibly know the things Tobi knew at that time.
7 Again anyone in the manga could plausibly do this and Obito would again be unlikely to do so.
8 This is a dumb point. Kishi covered his face because he wants people 2 ask questions and dumb people like u throw stupid theories like this out there.