he must be be somehow adopted by his parents.
Yep... but A God like enemy like that ... wonder how in earth will Naruto win......
Geez, so many theories flying around.
As for the question as to why Tobi needs both a Sharingan and a Rinnegan, it's probably because his Rinnegan 6 Paths techs don't stack on top of EMS techs like Madara's does. Tobi's Rinnegans must have been created differently from Madara's, or else Nagato would have used more than just his 6 Paths techs.
And no, Madara never met Oro. He knows about Impure World Resurrection because he knew the Second Hokage used it, which is who Oro copied it from.
Kwasi brought up some very good points. It can't be Itachi and Sasuke's dad because he would have never helped Itachi destroy the Uchiha clan, and it's probably not Obito because he never harbored bad feelings towards the village. And as someone else mentioned, it can't be the First since he was clearly proven to be dead during the Chuunin exams.
AND "THAT JUTSU" FUCK YEAH!
we never really saw madara use any magenkyo sharingan techniques did we? makes me wonder if he's even capable to go into that mode. thinking about it, he's shown as much jutsus as naruto has before his rasengan variations. he's only got the whole intagible thing going as well as the warping technique. his third would be the summoning of the gedo manzo. based on that, he looks more like an uzumaki than an uchiha.
From Kisame's talk, Tobi has been Mizukage as well.
This guy's fucked up the Fourth, Kushina and Kyubi, survived Itachi's Amaterasu and Konan's "wrath", controlled Nagato (why the hell did he attend Nagato to use his resurrection technique on him?), owned the First power by creating Zetsus. He's been a real mastermind until now. Hope he's gonna pawn Kabuto so far.
Plus he's got all the Uchiha's eyes that still remains from the massacre. I don't know what he's gonna do with them (Izanagi would be lame, maybe his Moon Plan)
Madara or not, he's already pretty much on the same scale than the First or Madara: a legend.
Has it been explained somewhere why Shisui hasn't been resurrected?
It's a Kishi hack. He only said Kabuto couldn't because Shisui fighting would have made the war horribly one-sided.