I think he's Christian Shephard. Look at Jacob in the few frames that you can see him, and his hair looks pretty similar. Also, I've seen comparisons with the eye that's seen and Christian's eye and they look the same. He has a deep voice - like the one that says "Help me". His coffin is empty, he's been seen by Jack on the island... it all adds up.

As for him being dead, the producers have said that they "may be using the word 'dead' in a sense we [the audience] don't fully understand yet."

He looks and sounds nothing like him >_>

I was wondering if the black smoke thing was one of Jacob's "forms". Kinda crazy and there's no basis for this theory. But ghost seems pretty close too, so I'll go with that.

I thought that too, or at least I think it may be the same thing as all the visions of people/things from peoples past, like Jack's father, Hurley and 'Dave' and other things.

giovanni_wasto that is some crazy suggestion there...... but i kinda like it!

I think it's an older Locke, i only watched it once but it looked/sounded similar to him to me.

Something Else! Jacob is a telekinetic figimagicthingabob - officially TV's wierdest mystery apart from the Black Smoke Monster - that freaks me out too; and I still dont get the whispers although there are a few theories floating around on that. But as for Jacob & BSM, I havent seen any concrete theories that definately match their explanations. I dont think Jacob will be something as simple as a Ghost a Holographic Projection or a Poltergiest. Ben? I dont see how he can be Ben?

Are Ghosts nd poltraguists the same??? nyway i think its the black smoke as it cn morphe to any thing!!

I think its something else entirely. I think a ghost seems a little far fetched even for Lost.

I think it's Christian Shepard too !

I have no clue.

I think that Ben just made him up basically.
xXx

I have been looking some screen shots of jacob for 'man behind the curtain' and i actually think he looks a bit like kelvin inman, the guy desmond was in the hatch with, have a look and see if u agree.

IMO lol Obviously Jacob is dead cos the whole episode was Ben seeing his dead mother on the island when nobody else could. Locke just cant see dead people lol

A Michael Emerson interview suggested this...

Well, a lot of choices vanished just then...:-O

Could people please only add answers that are an actual answer instead of "I don't know" or "Something no-one could guess".

I think is the black smoke. I don't really know why... =)

yeah, who/what the hell is jacob????

Im tired of guessin

I think that it's the ghost of the one who was the first one to find the island and then got kiled by the black smoke and now is stuck on the island or something
I don't think it's true but it's the best i can come up with

I auctually think it's Jack's father. In season 1 Jack saw him on the island. He might have been seeing things or he was really there. And when Ben took Locke to see Jacob, when we saw him he looked like he was in a suit.

kinda like the spirit or ghost of the island.

hhaha

I believe it's him!

This Jacob is rideculos! crap

A ghost would be to easy.

I think this is a very interesting theory.
I don't really think that it could be Christian because it seems that Ben has known about Jacob for quite a while, long before the plane crash. The plane crash would have "brought" Christian to the the island, and Ben had to know about Jacob before that.
The island theory could go in a lot of different directions...

I've always thought Jacob to be the island - whatever the hell thats going to mean

Who the hell said the black smoke?? Hahah, seriously come on

I think Jacob is the spirit of the island, comprising all of the apparitions including the smoke monster.

i wonder what or who too!?

Jacob is Jacob, a guy who can't die from natural causes and lives to protect the light in the center of the island. There ya go.