As per Lost and all of the twist and turns the show puts us through, I thought it was fitting to theorize on what is MIB's name. Some say it may be Wallace, some say Esau. But I think I know what his name is. And it makes sense since it hasn't been revealed yet.
I think his name is Jacob.
I think he is the dark side of Jacob while the Jacob we have come to know is the light side.
I think they are basically opposite sides of the same coin: an internal struggle.
Some key points:
1) MIB takes the white rock off of the scale and throws it into the ocean. Reason being: the light Jacob is dead and now there is no longer a white rock to balance the scale.
2) MIB tells the remaining Others at the foot of the Statue that he is disappointed in all of them. That's important because if the Others are Jacob's people, why should he be disappointed? He would only be disappointed if he had expectations. Expectations because he was once their leader and was replaced by the light Jacob. Maybe Jacob and MIB were fighting to control the Others and light Jacob eventually won. Now dark Jacob is in control with light Jacob out of the picture.
3) MIB was probably locked in Jacob Cabin. For the greater part of the series someone had been trapped in the cabin. Perhaps Jacob was trapped in the cabin all along, just the dark side.
4) Dogen tells Sayid every man has a light and dark side to him. The balance of the internal scale determines how good or evil one is. Who is to say Jacob is any different?
5) There is still a lot of mystery behind the origin of Jacob himself. Perhaps this has been withheld because there is a strong tie in between the light and dark Jacob and their collective antagonism.
6) A recurring theme of the entire series has been the struggle between light and dark. One of the first references to this struggle was the game of Backgammon. Notice how light and dark battle on a game board which could be a metaphor for Jacob and MIB on the island. But it could be interpreted as the light and dark pieces exist within the enclosed game.
There are other key points that I may add when I recall them, but that's it for now.