How does Jack change throughout Lord of the Flies?

In the beginning of Lord of the Flies, Jack is introduced in chapter one as being a very powerful leader of the choir. His authority over the boys is evident by the way the boys are still wearing their wool uniforms, even though the tropical beach setting would be more conducive to less restrictive clothing. They do not remove their togs until he tells them they are allowed to do so. Even when Simon faints,...

In the beginning of Lord of the Flies, Jack is introduced in chapter one as being a very powerful leader of the choir. His authority over the boys is evident by the way the boys are still wearing their wool uniforms, even though the tropical beach setting would be more conducive to less restrictive clothing. They do not remove their togs until he tells them they are allowed to do so. Even when Simon faints, the boys do not break form and sit down until Jack gives them permission to do so. Jack uses his power to maintain the order and expectations of the proper, civilized school to which they were accustomed. 

By the last chapter of the book, Jack is no longer using his authority to maintain the expectations of civilization. Instead, he is ruling by force and using his power to encourage savagery in its most evident form: the pre-meditated, ruthless murder of Ralph. The authoritarian nature of Jack's personality is consistent throughout the novel. However, it is the motivation of his character that changes drastically. Jack changes from being a leader that upholds the conventions of society to being a leader that actively destroys the conventions of civilized society.