Remember when Desmond was explaining his disappearance and sudden conversion to his jilted fiancee? He said that he was drinking and blacked-out, and when he came to a man with a rope tied around his waist was giving him a hand, which implies that it was one of the monks from the order that he joins. However, who do we know that also wears a rope around his waist? The Man in Black.
I'm thinking that MIB was active in Lostie world getting people to come to the island, such as causing Desmond to literally give up everything for a higher purpose. Maybe he was also the one who smashed up Locke's teenage mom with the car. Maybe he was Kate's horse. I'm sure you can think of others. So, all of those were his moves in the game. Next came Jacob's turn, so he goes and does his influencing. What think?