Who and What are the forces working against Bod Owens?

The major force consistently working against Bod Owens in
The Graveyard Book, by Neil Gaiman, is represented by Jack.  Jack
belongs to a group called Jack of All Trades.  Jack is one of the five Jacks that
comprise this group.  Their mission is to destroy Bod's family because of a prophesy
that indicated that a member of Bod's family would lead to their destruction.  After his
family is murdered, Bod as the sole survivor, crawls into a nearby graveyard where
ghosts and ghouls care for him and educate him.

Jack
presents an evil force throughout the novel.  Because of the way the inhabitants of the
graveyard treat Bod, we know that his life is in danger.  But the novel is also a story
of Bod's education.  He learns much about the world of the dead, the tricks of the
ghosts, and the habits of ghouls.  In these lessons, Bod is often in conflict with
himself.  He is not sure whom to trust or fear; he at times resists instructions; and he
is often reminded that he is the only mortal in a world of immortals.  Eventually, we
learn that the dead are helping Bod, rather than working against him, but this fact is
not always evident to Bod, or to the reader.