There has been many theories and debates on who Christians is actually "working" for, and I know a lot of you have heard this theory before but I going to see if I can tie up all the evidence I see to support my theory and neatly as possible...
Christian, the Monsater, and the Man in Black are all related
Proof?: - Someone else has been living in "Jacob's" cabin, theoretically, the Nemesis. ***Christian talked to Locke in this cabin and, theoretically, attempted to set into motion the events that would allow the Nemesis reappear as Locke by telling him to move the Island. - When Ben was being judged by the Monster, Un-locke conveniently leaves seconds before the monster appears and re-appears once it's gone. ***Also, the monster (as Alex) tells Ben to obey Un-Locke's every word even though it SHOULD know that he isn't really Locke.
- The Producers have already confirmed the the apparitions of Christian are related to the Monster.
- Christian, Un-Locke, and the Monster have never been seen together OR have ever really "existed" at the same time. ***I have yet to see an example of any two of them being in two separate places at the EXACT same time.
So basically, in a nut shell, this is ONE theory that ties three important aspects of the show together. I'm not saying this is undeniable proof, but I would assume one theory that ties things together is more plausible than three separate theories in explaining three important aspects of th show.