Locke / Smocke / Flocke / UnLocke / Esau / Smokie / The Monster / Cerebus / The Black Smoke/ The Man In Black / Nemesis
We know him by many names, and there is no real telling what his real name is, assuming he actually has one. I do beleive he has a name but I don't think we'll find it out for at least a couple of episodes, if not til the very end of the series. For some reason this is the mystery I want most solved.
I've heard various theories thrown out and this is my mish-mashed polished-up version of MiB theories.
In the most recent episode, Ab Aeterno, MiB says that Jacob stole his body. I've heard various theories floating about that MiB and Jacob may in fact be the same person, split into to. I personally think this would be a great twist. Richard can't kill himself, he has to have Jack light the fuse. In the same respect MiB couldn't kill Jacob because he IS Jacob, so he had to have Ben do the killing instead.
Jacob didn't really "steal" MiB's body. I think maybe in the far off past some traumatic event occured splitting apart Jacob into two beings. But scince there was only one body, only one of those beings could have that body. Jacob was split into his pure good side and his pure evil side. The good side ended up getting the body. The evil side was then forced to be manifest in the physical form of "evil incarnate" that being the black smoke. Ever scince MiB has been forced to use others' bodies instead.
So what is MiB's name? I beleive it's Jacob.