Jack acts as a foil for Ralph in that we see Ralph’s characteristics of fairness, concern with social order, and concern for the future more clearly in light of Jack’s violence, savage actions, impulsiveness, and descent into anarchy. Their similarities are important, too, as they remind us that both darkness and goodness are a part of every man.
Just when you thought Jack was bad enough, Roger comes along and one-ups him. We dislike the things that Jack does, but we can see an innocent boy in there the whole time. Because of his connection to Ralph, we watch his descent into primitivity from a starting point we could all relate to. Roger, on the other hand, is a rotten apple from the start. He shows us that, while in many cases darkness is part of man’s heart, in some cases that darkness is in control most of the time.