Why else would they not have told us his name yet? We've heard Jacob's name forever, and if MIB had a different name like "Isaac" or whatever they would have revealed it in 'The Incident', or at least some time this season. For some reason they are keeping it under wraps, so I think it has to be someone we already know, possibly having something to do with time travel. Who could it be? Aaron? The other half of Jacob? What do you guys think?