Re: LOST Season 6 -- All Good Things Must Come To An End
No I'm pretty sure Smokie IS Jacob's Brother...in spirit. He died, I think that much is clear, but his spirit or whatever IS the smoke monster.
I think Smokie has to be Jacob's brother. If Smokie was separate from Jacob's brother, it wouldn't make sense because why would Smokie follow the rule that he couldn't kill Jacob or the candidates when that rule wouldn't apply to him? As far as we know it only applies to Jacob's brother, not those who take the form of Jacob's brother, not to mention when Smokie takes the form of Locke he doesn't act anything like Locke, and so on. Throughout the show Smokie ... in whatever form ... has had to manipulate people to do some of the dirty work that he is forbidden to do (i.e. get Ben to kill Jacob). We also know he has manipulation skills from living with the other people when he was younger. That, combined with his desire to leave the island--as we know Jacob's brother wanted to do--IMO, Smokie has to be Jacob's brother.
Now, is it really clear his brother died? Heck, is anything in this show ever really clear?

Jacob said he had no intention of killing his brother before throwing him in the stream that took him down The Source. Jacob was also forbidden from killing his brother, so maybe he just knocked him out but didn't kill him before sending him down that stream. His brother's body may be dead, but it appears he is alive as Smokie. Maybe The Source killed his body (technicality)?
Now how he transformed in to Smokie (other than he went down a hole and magically came out as Smokie) is another question. And does he possess some ultimate evil now? We've been told if he leaves the island it will pretty much be the end of everything, but, unless I'm just forgetting at the moment, we haven't been told why or how that is. They were told never to go down the hole, he did, and now everything could cease to exist or something if he were to leave the island.