I posted this theory in another forum after the end of season 5 but since it is 'lost' there and very difficult for someone to come across I thought i should post it here as well..
We all agree I believe that at this point of the series there is a high possibility that the Mystery Man as some people like to call him is the smoke monster.A shape shifting entity that can take the form of people that are dead and whose dead body is on the island..So..this way he can have an anthropomorphic form and besides that interact with the people on the island and strategically create circumstances that favor him..Of course when he takes the form of a human he not only has his memory but also his name since he is bound to the consciousness of that person and he has to eat(something that would otherwise be strange for an entity that has no physical form).We have seen this three facts in the series,fist of all when he took the form of Lock he had his memories,secondly when he was Christian he said to Lock "I am christian" and also "say hello to my son" and thirdly both he and Jacob have to eat as we have seen at "the incident"...
So assuming that all this is true the most logical and possible thing is that Jacob is an entity of the same nature,a White Smoke entity and that these facts apply to him as well...
Now..the statue is Sobek which in ancient Egypt was depicted as a crocodile or a man with the head of a crocodile and was a powerful and frightening deity,in some Egyptian creation myths, it was Sobek who first came out of the waters of chaos to create the world. As a creator god, he was occasionally linked with the sun god Ra.The opponent of Ra is Apep,the god of evil who is a giant snake(so MM,the "monster" is probably apep or something very similar which is part of the lost mythology and in that case I can't guess),Ra is the bringer of light..So a logical conclusion is that Jacob is Ra the nemesis of the monster and the two of them are engaged in a short of "divine war"..Besides that Ra was thought to travel in a sun boat (the island.?) to protect its fires from the primordial waters of the underworld it passed through during the night,since nearly everyone can see that the sun is not attacked by a giant snake during the day, every day, storytellers said that Apep must li! e just below the horizon.. This appropriately made him a part of the underworld(the smoke monster is hiding underground as we have seen in the series,for example when it was pulling Lock), which attacked the sun each night,Apep tried to stop the sun boat's journey every night by consuming it.
Again if the above are true then we start to make guesses and observations...Firstly if Jacob is a White smoke entity specifically Ra then he should have the general form of a falcon(as the smoke monster has the general form of a snake) because Ra is associated to the falcon..And thinking about this I remembered the strange bird that flew over Hugo and the others (in season one I think) which was relatively small but we have seen the monster in various sizes from enormous to a very small amount of smoke passing by or observing so size doesn't matter...Again if they are both taking forms what form did Jacob take?One obvious answer is Vincent as many have said before,but there is an other one that I had forgotten all about and because of a clip in a video I remembered...When Lock went to the Cabin there was christian(MM) and Claire..So what if Claire is actually dead,maybe due to a Rousseau's trap (that could also be the reason why Aaron was alone in the jungle) and that was J! acob....I mean the island was threatened by outsiders so what if the 2 of them collaborated to save the island..?Someone might say but Claire is a girl.!So?Is Jacob a man?No,he is an entity of higher intelligence an of a form that is at least of a high evolutionary state(I'm not taking this to a religious level because I am a physicist and thus not a very religious person but anyone can think of their nature anyway they like at least until we are sown what they are..).
So in conclusion the 2 of them are playing a "game" a game that has been going on for thousands of years and we(people)are not intelligent enough to perceive..The people on the island and the others are their pawns.I don't know and don't want to guess he details and origin of the 2 of them because that would be just guessing and besides that I wait for the series to show me..So finally I believe that in season 6 we will have the appearance of the White Smoke(Jacob,Ra..etc),maybe that is the true meaning of the white screen at the end of the episode.
P.S. This makes you think of something else..Are they Apep and Ra?Or did the ancient Egyptians accidentally find the island and inspired by the 2 of them created the gods Apep and Ra?And also if The white smoke entity took the form of Jacob after he (Jacob) was dead,is Jacob a historical person or someone who was just on the island or brought to the island...?
P.S.2 The fact that the smoke monster is a snake can be realized by a detail in the series that always troubled me and now can be explained I believe.I always wandered why the smoke monster could not pass the sonic fence,I mean the fence is only 2-3 meters tall and we have seen the monster sort of fly..But that is not the case probably,since it is a snake it can only crawl or hover close to the ground..