A JINN THEORY

This is a Jin theory, but not a character based one.

Ancient cultures had beings called jinns who bridged between the human realm and the spiritual realm. They were described both as beneficial and evil. But in most instances, they came to people as messengers.

In Arabian and Muslim folklore jinns are ugly and evil demons having supernatural powers which they can bestow on persons having powers to call them up. In the Western world they are called genies. 

Legend has it that King Solomon possessed a ring, probably a diamond, with which he called up jinns to help his armies in battle. The concept that this king employed the help of jinns may have originated from 1 Kings 6:7, "And the house, when it was in building, was built of stone made ready before it was brought there, so there was neither hammer nor axe nor and tool of iron heard in the house, while it was in building." 

In Islam, jinns are fiery spirits (Qur'an 15:27) particularly associated with the desert. While they are disruptive of human life, they are considered worthy of being saved. A person dying in a state of great sin may be changed into a jinni in the period of a barzakh, separation or barrier. 

The highest of the jinns is Iblis, the prince of darkness, or the Devil. The jinns were thought by some to be spirits that are lower than angels because they are made of fire and are not immortal. They can take on human and animal shapes to influence men to do good or evil. 

They are quick to punish those indebted to them who do not follow their many rules.

In the "Arabian Nights" jinns or genies came from Aladdin's Lamp. 

There are several myths concerning the home of the jinns. According to Persian mythology some of them live in a place called Jinnistan. Others say jinns live with other supernatural beings in the Kaf, mystical emerald mountains surrounding the earth.

There are many traits of genies in the show:

1. the smoke monster could represent a fire spirit and in the end, MIB was not immortal.
2. the events on the island were important to bridge the character's sideways lives, so the island could be considered a barrier world where jinns would occupy and help humans.
3. jinns don't follow rules and neither did the characters or the show's writers.
4. characters made several references to the Devil in the show, including towards Jacob.
5. the smoke monster could take on human and animal shapes like a jinn.
6. the island characters such as Jacob, MIB, Alpert, all tried to shape the castaways to do good or evil.

Throughout LOST, there were messengers in the form of flash back visions of things on the island, dead people giving characters information or direction, but at other times the past visions turned violent like with Eko's talk with his dead brother, Yemi, who turned into the smoke monster.

In Western fairy tales, a Genie in a bottle could mean a smoke like creature with intelligence and magical powers to grant wishes. The island could have been that bottle. It's "cork" was released and then re-set to capture the smoke monster apparently in human form. And the island in many respects did grant the characters wishes - - - such as Locke being able to become an outback hunter and leader; to Jack reconciling with his father. The island could have been one great second chance granted by Jacob, a jinn, to his candidates.