Jacob is the Man in Black's father by moosewizard

It might be ridiculous to think about, because MIB *looks* older than Jacob, but then what's to say Titus Welliver was MIB's initial form?

But hear me out. What has been one of the most predominant recurring themes on this show? - Parental Issues, specifically, daddy issues -- beginning with season one episode "All the Best Cowboys Have Daddy Issues." (SEE: http://lostpedia.wikia.com/wiki/Daddy_issues)

Furthermore, if the MIB and Jacob are related, it could definitely explain MIB's animosity towards Jacob. His "creator"/"father" won't let him leave the Island and has relegated him to a specific task (to protect the Island). He is stuck there -- like a child with a curfew or a kid who has chores. All MIB wants is to be free. But Jacob is also trying to protect the outside world from his "child," in the same manner that Dr. Frankenstein realized that his monster wasn't fit for society, or Prospero teaching Caliban English turned Caliban against his very nature (causing Caliban to resent Prospero).

Jacob also doesn't seem to have any animosity towards MIB -- at least, not in the same way that MIB hates Jacob. Perhaps because Jacob loves his "creation"/"son" just like any father, but unfortunately his son can turn into smoke and is incompatible with society.

In addition, if this holds true, it would also make MIB and Locke's storyline's parallel. Locke got Sawyer to kill Anthony Cooper for him, in the same way MIB got Ben to kill Jacob for him. So there would be some thematic unity.