Explain the relationships between Jack and Piggy in "Lord of the Flies."

Jack, a tall, strong-willed, forceful ego maniac takes an immediate dislike to Piggy. 

"Piggy is a man of thought, not of action, and he is physically weak because of his asthma."

When Jack looks at Piggy, he sees everything that a typical bully loves to pick on, an overweight kid, with glasses, who doesn't like to fight and can barely defend himself against an insult.

From the start, Piggy is fearful of Jack, who after he strips away his last sense of civilized propriety, oozes with savagery.  He is frightening to be around, and Piggy makes sure to stick with Ralph. 

Jack tolerates Piggy in the beginning, but his clinging to the rules of civilized behavior start to irritate Jack as the novel progresses.  

As Jack becomes more detached from any form of social order, and assumes a primal nature, he and Ralph begin to fight.  The disputes encourage Piggy to insist on rules all the more.  This further separates Piggy from the group and ultimately the disconnect between the boys results in the death of Piggy.