Well obviously no one knows... or very few people know (I still think that there are a couple original bitcoiners on this forum who are 99% sure that they know who Satoshi is).
Whats your favourite theory?
Mine is that it was John Nash

Please provide some proof for your theories. Would love to look into them!
Well one thing I am certain of is that he is either dead or he lost the private keys to his wallets, its inconceivable that every single wallet identified as his has never had a single satoshi transferred since he disappeared.
Going with the theory that he is dead the most obvious answer is Hal Finney.
I still don't see why no one goes with the obvious theory, he wiped his drives and deleted all of his private keys.
Gavin, told him that the Federal government wanted to meet and he quickly realized what was going to happen, they were going to force him to build a back door and make bitcoin closed source (or something along those lines) or charge him as an accessory to every single drug transaction on the silk road.
At the time deleting the coins was probably a very wise financial situation vs fighting tooth and nail to stay out of prison, especially with very little known about cryptocurrency at the time.