Jack's character changes dramatically in Lord of the Flies, evolving from proper choir boy to full-blown vicious savage.
Jack enters the story as a choir boy, still with full choir regalia. His claim to leadership among the other choir boys is that he is "chapter chorister and headboy" and "can sing C sharp" (22).
As the story progresses, Jack's persona shifts from that of choir boy to hunter and savage. A defining moment occurs in chapter four when he makes the painted mask on his face, "a thing on its own, behind which Jack hid, liberated from shame and self-consciousness" (64). Jack's savage side emerges, ready to hunt and kill. "The mask compelled them" (64). Jack becomes known for his expertise and daring in the hunt, for he is able to take the savagery to the next level and kill the sow. The other boys both fear and respect Jack, much in the same way they did for his ability to sing C sharp--only now it is Jack's affinity for violence that defines his leadership, not his musical ability.
By the end of the novel, Jack's transformation to savage is complete; at the death of Piggy, Jack is jubilant in his authority:
"See? See? That's what you'll get! I meant that! There isn't a tribe for you anymore! The conch is gone [...] I'm chief!" (181)
Even though Jack did not kill Piggy himself, his acceptance of the outcome reveals his commitment to violence as a force of strategy and leadership. Jack shortly after orders the death of his rival, Ralph to assure his own dominance as chief over the island.