Maybe MIB's Origins and other etc... by LPFreak64

This might explain a little back story. It sounds right to me! Help me find some loopholes, I know they are there!!!

The Man in Black and Jacob are brothers. They are brought to THE ISLAND by the current leader of an ancient tribe on The Island (THE OTHERS). Jacob and the Man in Black join the tribe and live in THE TEMPLE. The tribe are the Guardians of The Island. The Island is a kind of purgatory for souls that can not go on to heaven or hell.

The souls are kept on The Island by an electromagnetic field naturally produced by The Island. There are pockets all over The Island from where the field is too close to the surface (THE
WELLS, SWAN STATION). Due to the electromagnetic fields, any baby that is conceived on The Island dies before it is born. Thus, the leader brings new people to The Island in hopes of them joining their ranks.

Jacob and the Man in Black grow up as best of friends as the community teaches them THE RULES on guarding souls and how not to break them. They teach them about how they elect a leader through a series of tests (The Candidates). The leader is in charge of electing a new leader and of keeping the souls on The Island.

The Man in Black grows up and becomes friends with one of the souls on the Island. He begins thinking that it is not fair to keep the souls in purgatory forever and he decides to become leader to change THE RULES. But not only is the Man in Black running for leader, but so is Jacob. It comes down to Jacob and the Man in Black. Jacob somehow sabotages the Man in Black and Jacob becomes the new leader.

The Man in Black is outraged. He goes home and in his anger, accidentally kills his and Jacob's mother. This is an act punishable by death. Before the Man in Black can get rid of the body, Jacob arrives and discovers what his brother has done. The Man in Black is executed the next morning. He becomes a soul trapped on The Island. However, seeing how he was a candidate, he has special powers (SMOKE MONSTER, SHAPE SHIFTING).

This is why the Man in Black says that Jacob "stole" his body. This also fuels the Man in Black's desire to get off The Island. He knows The Rules and he begins looking for a loophole.

This is about as far as I could get before my brain decided
to die....I'll write more soon.