Jack represents evil and violence, the dark side of human nature. A former choirmaster and "head boy" at his school, he arrived on the island having experienced some success in exerting control over others by dominating the choir with his militaristic attitude. He is eager to make rules and punish those who break them, although he consistently breaks them himself when he needs to further his own interests. His main interest is hunting, an endeavor that begins with the desire for meat and builds to the overwhelming urge to master and kill other living creatures. Hunting develops the savagery that already ran close to his surface, making him "ape-like" as he prowls through the jungle. His domain is the emotions, which rule and fuel his animal nature.
The conflict on the island begins with Jack attempting to dominate the group rather than working with Ralph to benefit it. He frequently impugns the power of the conch, declaring that the conch rule does not matter on certain parts of the island. Yet he uses the conch to his advantage when possible, such as when he calls his own assembly to impeach Ralph. For him, the conch represents the rules and boundaries that have kept him from acting on the impulses to dominate others. Their entire lives in the other world, the boys had been moderated by rules set by society against physical aggression. On the island, however, that social conditioning fades rapidly from Jack's character. He quickly loses interest in that world of politeness and boundaries, which is why he feels no compunction to keep the fire going or attend to any of the other responsibilities for the betterment or survival of the group.
The dictator in Jack becomes dominant in his personality during the panic over the beast sighting on the mountain. In trying to get Ralph impeached, he uses his rhetorical skills to twist Ralph's words. In defense, he offers to the group a rationale that "He'd never have got us meat," asserting that hunting skills make for an effective leader. Jack assigns a high value only to those who he finds useful or agreeable to his views and looks to silence those who do not please him. Denouncing the rules of order, Jack declares, "We don't need the conch any more. We know who ought to say things." He dictates to his hunters that they forget the beast and that they stop having nightmares.
As Jack strives to establish his leadership, he takes on the title of "chief" and reinforces the illusion of station and power by using the other boys ceremoniously as standard bearers who raise their spears together and announce "The Chief has spoken." This role is no game for him, though; by the night of Simon's death, Jack has clearly gone power-mad, sitting at the pig roast on a large log "painted and garlanded . . . like an idol" while "[p]ower . . . chattered in his ear like an ape." His tribe addresses him as "Chief," indicating a form of more primitive tribal leadership.
True to Piggy's assertion that "It's them that haven't no common sense that make trouble on this island," Jack takes an entirely different direction from logic or common sense. Perhaps acting out of some guilt he is unable to acknowledge, Jack becomes paranoid and begins feeding misinformation to his tribe, a typical practice of dictatorships to control the collective thinking by controlling the information that is disseminated.
Given the thrill of "irresponsible authority" he's experienced on the island, Jack's return to civilization is conflicted. When the naval officer asks who is in charge, Jack starts to step forward to challenge Ralph's claim of leadership but is stopped perhaps by the recognition that now the old rules will be enforced.