I will try to make this short because I am more interested in what people think about the idea rather than trying to predict exactly how this will play out.
My theory is Christian and UnLocke at 2 separate people (or beings or entities whatever) due to the fact that after flight 316 crashes they both seem to appear at the same time in 2 different places. 1) Christian appears to Sun and Frank while 2) UnLocke appears to Ben.
Also, I believe there might be 3 or even 4 entities on the island. Granted they may not all be playing on separate sides some might just be in it for helping the survivors not Jacob or MIB/UnLocke. I believe these entities to be;
Christian Shephard (Christian when he is wearing the suit)*may be the same as unlocke
UnChristian (Christian as he appears the majority of season 4 and 5)*may be the same as unlocke
Now that I have explained why I think Christian's appearance and UnLocke are different entities, here is some BS as to why I believe the 2 appearances of Christian are different entities, I'll try to keep them in order of time rather than season.
1.Christian appears in a Suit to Jack and leads him to the caves(Season 1)
2.Christian appears in a suit (same as prior appearances) to Hurley (Season 4) **see note below
3.Christian appears holding Aaron in a dress shirt no suite
******This was the first time that Christian was seen on the Island without his blue suit—instead, he appeared to be wearing a dress shirt.
4.Christian appears in the same shirt again to Locke inside Jacobs Cabin (Season 4) **see note below
5.Christian appears in the same shirt to Michael on the Freighter (Season 4)
6.Christian appears in the same shirt to Locke before he moves the wheel (Season 5)
7.Christian appears in his original suit to Jack off the island (Season 4)
8.Christian appears in the same dress shirt to Sun and Frank (Season 5)
**Now I am very open to the idea that one of these Christians could be the same as UnLocke, but I believe the changing of his outfit from suit to different shit and back will play a significant roll especially the fact he was seen in the cabin in a suit as well as a dress shirt.
I am sorry if this has been said before I read this site everyday and I don't remember anyone bringing up I think most people over looked the outfit change and the fact Christian was appearing to Frank and Sun at the same time Unlocke appeared to Ben.
WHAT DO YOU GUYS THINK!
**UPDATE: I also wanted to make note that if Christian in a dress shirt is unlocke, that I found it interesting that he did not "touch" or help john when john went into the well, since Jacob touched 5 of the oceanic 6 as well as Locke. Maybe the man in black cannot touch someone who Jacob has physically touched. That is why he was able to hold Aaron but not help Locke.