Jack has always been an ill-natued boy even from the start of the book when he told Piggy to "Shut up, Fatty." (p.23). Despite Jack's unpleasent personality, his lack of courage and his conscience preventing him from killing the first pig they encountered. "They knew very well why he hadn't; because of the enormity of the knife decending and cutting into living flesh; because of the unbearable blood." (p.34)
When Jack was chosen to keep the fire going, he decides to get meat instead of tending to the fire. His pursuit for killing a pig is symbollizing a sexual desire built into human nature. While he was out pursuing the pig, the fire went out. This symbollized the fact that Jack's sexual desires led him away from hope and deeper into despair.
Jack represents a Satan like, deathly force. The blood that he wallows in is a further representation of deathliness. After his first kill, "Jack transferred the knife to his left hand and smudged blood over his forehead as he pushed down the plastered hair," he unconsciously imitates the ritual of the tribal initiation of the hunter, whose face is covered with the blood of his first kill.
Jack then successfully convinces many big'uns and little'uns to come along with...