I believe that "Jacob's Enemy", i.e. the man who talks to Jacob in the opening scene of The Incident Part 1, can take the form of people who are dead, when their body is on the Island, like a chameleon. He started impersonating Locke when his body was brought back to the Island.
Also, I believe he is also impersonating Christian Shepperd. Ilana said that someone else than Jacob has been using the cabin and Christian Shepperd's body is on the Island. If this is true, it would mean that he's the one who told Locke to Move the Island.
I also think that he was impersonating Alex when she told Ben to do everything Locke would tell him. Please note that, at that time, Locke wasn't with Ben even tough they went to the temple together. How convenien…Read more >