InLord of the Flies, the most obvious change in Jack's character concerns his appearance. He is introduced in a formal outfit which clearly identifies him as part of a civilized group. Specifically, he is dressed as a choir boy.
As the novel goes on Jack removes most of his clothes and begins to paint his face. In doing this we see the second change in his character as he gradually pulls away from the group. For a brief moment, Jack is alone on the island, painted up as a hunter, living without rules.
This is his third significant change. Jack begins as a proponent of rules and order but eventually chooses against rules, democracy and civility in favor of animalism and chiefdom.
From an orderly choir boy who is part of the group, Jack becomes the leader of a lawless and informal group, painted up in a rude costume of charcoal and chalk.