In the beginning, Jacob and Esau - two brothers, perhaps - were very close friends. Together, they got to rule the Island (how isn't explained in this theory; perhaps they were to normal people who stumpled upon it and thereby got "supernatural" powers, or sent their by some Egypt god, or was born their and was the heirs of the Island as their parents ruled it before, or... well, it isn't really relevant to this theory; I just assume, for the sake of this theory, that they a very long time ago somehow got in charge of the island). Who they were, and what the nature of their powers were (if they had any powers of their own - perhaps they only were able to use the Island's powers?) this theory doesn't explain.
In order to avoid future lethal conflicts (even the best friends could turn against each others after having to be together a very long time), Jacob and Esau created a contract. But it wasn't an ordernar, easily-breaked contract. It was something that could be called an "Island contract". An Island contract is unbreakeable by makers of it; the Island perserved it. More on this soon.
On the Island, a strange creature lived. They called it Cerebrus. Cerebrus was very gifted, and perhaps unique in it's kind; it (I use the word "it" for ease; indeed, it's something more than just an object) was like nothing else on earth. It had the ability to shape shift, and read people's memories... perhaps even their current thoughts. It isn't easy to tame Cerebrus, but once one manages to, it remains lojal to one. Jacob and Esau managed to make Cerebrus follow them, and it was
They both shared a vision: creating an utopian society. What would be the best place to create it, if not on the Island, with it's (perhaps/seemingly) supernatural abilities, a place yet uninfected by humanity's greed and civlization? They had such a beatiful plan, but just to make sure it wouldn't fail, they created an Island contract. This said that neither of them could kill the other. However, just to be sure (they needed to be able to kill one of them if one of them would turn evil), they left out a small room for killings anyway; they included, intentionally, loopholes. This loophole consisted of the allowing of any of them to kill the other, but not alone; they must convince the current leader in the utopian society that it was a good idea (as the leaders would be good people, it wasn't possible to kill the good one if one of them would turn out evil; the leader would never agree to do it).
So they started bringing people to the Island (with the use of the Island's special abilities, or perhaps any special abilities of their own) who would be part of the utopian society. But every time, their plan failed. The people started to fight, destroy... corrupt. It nearly seemed that human was to selfish, to limited to understand the specialness of the place, having to huge lust for power, to ever be able to live peacefully and happily on the Island. Jacob, however, didn't loose his faith in humanity. He was convinced that, eventually, their vision would be reaced. Esau didn't agree with him; after every failed attempt, he got more and more unsure to wherther man actually could form an utopia. He started getting a little irritated on Jacob; why didn't he understand that perhaps they should give up their plan, admitting human after all weren't as good as they had thought and hoped, and do something better with the Island - perhaps instead of bringing those destroying hum! en to the Island, protect it from them?
Esau stopped bringing any more normal humen to the Island; instead, Jacob had to bring them their himself. After even more unsuccesful attempts to build the utopia by Jacob, Esau got more thann irritated, even angry, at him. His best friend, who always had been very wise and good, now dogmatically clang on to an idea that perhaps in theory sounded nice, but due to the bad of humanity, never would work out. How could Jacob so totally fail to see the obvious? But Jacob, in despise of unsuccesful convecing attempts made by Esau, didn't give up their - now only Jacob's - vision. And his arrogande towards Esau created a deep conflict between them, esaing - perhaps permanently their earlier so strong friendship. Esau loved the Island; therefore, Esau hated Jacob.
Jacob, on the other hand, wouldn't give up their beatiful vision that easy. Hadn't Esau agreed it would probably take some time to realize ther plan? And why would they give up now? They had eternity. And what Esau said about instead protecting the Island from humanity - well, it hadn't been totally destroyed or that badly infuenced by the people they brought there hitherto, and Jacob was willing to take the risk if chanses were the utopia would come true (he was convinced the Island would also benefit from the utopia; it would be more good for the Island having an utopian society on it, rather than only being used by two persons). Esau was not, and no matter what Jacob tried to do, Esau would cling on to that dogmatic save the Island from humanity-thought. Jacob didn't hate Esau for this; rather, he felt sorry for Esau's lack of understanding, Esau's divergent from the right way.
And yet another time Jacob brought people to the island, this time the ship the Black Rock. He did, that beatiful day in in the 1850's, his everyday routins; a little veawing, and then food. Sitting on the clff, he watches the Black Rock being not that far from the Island. Esau walks by. After they exchange greetings, Jacob offers Esau some fish, which Esau politely (for old times' sake) declines, Jacob declares his belief that Esau is there because of the ship, which Esau verify.
Esau then asks Jacob, "How did they find the Island?". Jacob, by some reason unknown (perhaps he didn't want to argue with Esau even more? but then, why start talk of the ship in the beginning?), simply answer that Esau probably gets the answer when they'll arrive on the Island. Esau, however, full of hatred in his voices, contradicts Jacob, telling the truth: "I don't have to ask. You brought them here." Jacob doesn't answer; instead, Esau correctly claims Jacob is still trying to prove him wrong, which Jacob immediatly and with certainity say Esau is.
Esau, retorically, asks "Am I?", and then, a littled depressed, gives his point of view on the bringning of people to the Island for the first time on screen: "They come. They fight. They destory. They corrupt. It always ends the same." Jacob,arguably wisely, changes subject a lttle: "It only ends once. Anything that happens before that is just progress.", indicating his view that eventually, the utopia will come true, and that whatever happened before that will be non-mattering history (which, however, was quite important for realizing the utopian society; at every failure, Jacob learns something new to think of in his next attempt).
The feeling of their conversation harden, as Esau, with ultimate disgust and hate, asks: "Do you have any idea how badly I wanna kill ya?" Of course, even though Esau hadn't admitted his wish before, Jacob had noticed how his former best friend had gotten more and more angry at him; the deliver was no shock for him. Therefore, Jacob simply answers, perhaps with a bit arrogance, "Yes.". Esau then tells him about his search for a loophole (a leader of their utopic society he can convince to kill Jacob). Esau thus perhaps wants the society Jacob is building to make the utopian, but even if it would be realized, he would want to kill Jacob (to, perhaps, later kill all the people in the society, so the Island would stay clean of humanity; it's his new principe that humanity on the Island NEVER can be good, no matter how "worthy" or "special" that specific humen are).
That is quite sensational; he had gone from liking Jacob and the idea of an utopia, to like Jacob and dislike the idea of an utopia, to dislike Jacob and dislike the idea of an utopia, to hate Jacob and dislike the idea of an utopia, and then, eventually, just hate Jacob and wanting to kill him for bringing so many unworthy people to the Island; at the time of the Black Rock arrival, Esau seemed to have partly left the ideological (Esau wanting to protect the Island, Jacob wanting to damage it by brining human there) reasons of the rivalry between him and Jacob, to instead think it had the rivalry had a worth of it own; nearly like a game.
They end their conversatoin by Jacob saying he'll stay right there, so Esau knows it when/if he finds a loophole. With a "Always nice talking to you, Jacob." (perhaps with a sarcastic undertone), and a nearly sad (Jacob seems to miss the good old days when they were friends rather than rivals) "Nice talking to you to", Esau walks away, leaving Jacob at the statue of Taweret. For how long, we don't know, but what happens next, I think we'll get to know (no matter if the above is correct) in season six.
The Black Rock arrived, with Richard (Ricardus at that time?) Alpert as one of the people onboard. Jacob tried to make them buld that utopa; Esau tried to get them to leave, or at least start fight among themselves (it seems like Esau no longer wanted an utopia at all, even if human could do it; he wants the vision to fail, because, on principle, he thought man couldn't be worthy the Island), possibly with the help of Cerebrus. Jacob found Richard worthy; finally, someone who could take the burden of leading the people to the utopian society (of course, the earlier groups of people have had their leaders, but not any special, good or worthy ones). Therefore, Jacob elected Richard as the first leader of the (hopefully soon-to-be-utopian) society. Even if Esau technically had the right to be co-desciding in the choise of leader, he gived up that Island contract given right; even if he could elect a leader he could convince to kill Jacob, he found the thought of having anything! at all to do with the society and Jacob so disgusting he rather bided his time. And if that Richard would turn out to be hard-convenceable, he could wait for later leaders (Esau correctly didn't think Jacob wanted Richard to be a permanent leader.)
Esau approached Richard. He tried, in all ways he know, to convince him, but what Esau didn't know, was that Richard had a special reason to trust and like Jacob. When Black Rock had arrived at the Island, Richard had got in trouble. There had been a mutiny, and Richard had taken the captain's side. On the Island the first night, there had been a huge fight between the quite many captain supporters, and the mutineers. The mutineers had won, killing the captain, and all the people on his side... they thought. However, Richard wasn't dead; he was just lethally hurt (a difference that, in a normal place, wouldn't have mattered the least, since he was beyound normal medical science curing; i.e., not even the best doctor could have helped him). The Island, though, wasn't a normal place, and there was other curing methods than the ones science recognized.
Jacob walked up to Richard, slightly touched the in pain writhening Richard on his forehead, calmly saying "Don't worry. You'll be all right.", and watched how Richard soon thereafter fall asleep. When wakening up, Richard was in a for him unknown place; the statue of Taweret. Jacob told him everything, and Richard agreed to become their leader for a time.
And Esau tried to convince Richard to kill Jacob, but he failed. The waiting for Esau for the next leader gets long. After a couple of decades, he notices how Richard doesn't look like he has aged a day; earlier, he thought it was just the feature some humen have (the abilty to look young even if they aren't), but clearly, Richard must have been helped by someone. Of course, Jacob. Angrily, Esau thought Jacob had changed his mind and wanted Richard to be the leader forever. But Jacob hadn't. Instead, he soon chose a new leader - some dump person who would blindly follow Jacob, Esau saw it. Jacob saw it as a good way of loosing a little of his control of the society - because his goal was that the utopian sociaty would be self-leading, self-working, not needing his constant watch over them, so that perhaps that life style would spread itself across the world, and in the end, the whole world would be utopian (if it would need him leading it, the plan of utopian societies every! where wouldn't work; he couldn't lead everyone).
And Esau tried to convince the new leader to kill Jacob, but he failed. But then, finally, in 1977, some easily-manipulated fool became the leader (Jacob had now given very much of the control over the society to the leader of it, including the right to choose leader; Esau had never claimed his right to choose leader, but, as I said, preferred to wait): Charles Widmore. The earlier leader, Eloise Hawking (who now moved out of the Island to raise her kid), had loved Widmore, and therefore was unable to see his faults as a leader. And Esau tried to convince Widmore to kill Jacob, and he succeed. Richard, however, got suspicous when Widmore asked to see Jacob, so he firstly told Jacob about Widmore and his own suspicions that he might have been manipulated by Jacob.
It was the last straw. Jacob got mad at Esau, and used all the powers and abilities he possesed to making Esau nothing more than a soul, or spirit if you want to, whose only power was the control he had over Cerebrus (along with Jacob's). Jacob imprisonated Esau in a cabin, surrounded by spirit imprisonating black ash. But Esau still didn't give up; he had left the reasoning, the logic, and the good behind himself, for madness, or pure revenge want. He did barerly even care about the Island; he only cared about defeating Jacob. He had to find his loophole.
When Jacob brought Ocenic Flight 815 to the Island, Esau constantly used Cerebrus' apperation ability in order to make the Losties do what he wanted them to do (and as he had become quite insane by his compulsory Jacob hunt, Cerebrus also did some unlogical things). When Benjamin Linus eventually led John Locke to the cabin (Richard had told Ben that was Jacob's real place, so he wouldn't seek Jacob up if he didn't really need to; Richard would never have thought Ben would actually go there, breaking the circle of ash), they broke the circle of ash. And Esau was free. He could take the shape of whatever person he wanted to... but only when the person had died.
The first person he took the shape of was Christian Shephard (earlier, he had only been able to make Cerebrus shape shift to appear as the form of Christian and other people to people; now, he actually took the body of Christian, and could freely walk around, seen by everyone; not as an apperation, as it was when Cerebrus took the form of people, but rather actually having that body). So Esau arranged things so that Locke would die and his body then turn up on the Island (he manipulated Locke's dream so he would find the cabin, and then - with Christian's body - told Locke he had to move the Island, so Locke would get outside the Island, there he without Christian's protection eventually would be killed and then his body would be brought back with the plane).
When Locke's body was back on the Island, he ordered Richard to take him to Jacob (if Jacob perhaps would have moved since Esau last saw him), and then conveinced Ben to kill Jacob. Had Jacob not been shaped as Locke's, Richard would not that lightly led him to Jacob but rather warned him, and Ben would never have listened to a stranger, if Esau would have taken another body than Locke's (he made Ben listen to Locke by using Cerebrus - appearing as Alexandra in the Temple - telling him to listen to Locke). Something I don't know is why Esau just didn't just Cerebrus to tell Ben to kill Jacob, and tell Ben where Jacob probably were. Hmm... Any ideas?
When turning up with Ben in the foot of the statue of Taweret, Jacob immediatly understood what had happened. But he knew Ilana's group was coming, and that they would kill Esau for him (as once he was gone, the Island contract wouldn't apply); Jacob hade been even more foreseeing and planning than Esau, as he had asked Ilana to show up on the Island so they could kill Esau once Jacob was dead. Jacob was ready to die; he knew that Ilana and her group would join his society, and that they would choose a new leader after Locke and Ben (that's what Ilana meant with "He might be a candidate." about Lapidus; Lapidus could be a candidate for the post of the leader). And with that new leader, and Esau and himself gone (so noone could, either willingly or by an accident, interfere with them), the society was ready to be utopian.
And his vision would come true.
(Originally posted on http://www.spoilertv.co.uk/forum/viewtopic.php?f=17&t=13979&start=0&view=viewpoll)