At first, Jack appears to be quite a normal boy of his age. Normal that is for someone of his elite, privileged background. Arrogant, lazy, and with an innate sense of his own superiority, Jack is not exactly the best advertisement for the English public school system.

For all of Jack's negative personality traits, however, there's no real hint of what's to come later. He may not be the most pleasant of characters, but there's nothing to suggest that he'll develop into the crazed, psychotic dictator that he'll become later on.

Nevertheless, there are signs early on that Jack represents, at the very least, a danger to Ralph's rules-based system of order on the island. It's clear from the get-go that this island isn't big enough for the both of them. After Jack fails in his bid to be elected in Ralph's stead as leader, he realizes that the only way he can exercise power is through the establishment of a dictatorship.

Up until this moment, we've seen Jack become more and more enamored with violence, not just toward pigs but also the other boys. Once his growing penchant for violence is cemented by his becoming dictator, Jack is effectively unrestrained. Now there's no one to stop him from doing what he wants. He can, and does, institute a reign of terror which results in the tragic death of Piggy and the persecution of Ralph, who's hunted down by Jack and his thugs like an animal.

All in all, one could say that Jack's personalty combined with the environmental factors of life on the island have turned him into a monster.

Towards the beginning of the novel, Jack is portrayed as an arrogant, selfish boy, who craves authority and attention. He is upset that Ralph is elected chief and develops a grudge against him. Despite Jack's antagonistic nature and willingness to talk over others, he is not fully malevolent or savage. He is, in the beginning, still capable of acting civil and attempts to reconcile with Ralph several times.

Jack is enthusiastic about killing pigs and quickly finds his identity as he leads the boys on hunting expeditions. As the novel progresses, Jack begins dismissing Ralph's commands and chooses to hunt wild pigs instead of completing various tasks necessary for survival. Jack's refusal to comply with Ralph's directives leads to several heated arguments between the two boys after Jack refuses to help build the huts and dismisses Samneric from their signal fire duties. After Jack experiences his first successful hunt, he quickly descends into savagery. Jack begins painting his face and openly opposes Ralph as the leader of the group. Jack continually argues with Ralph and physically abuses Piggy.

Eventually, Jack attempts to usurp power from Ralph but fails. Jack then establishes his own tribe of hunters at the other end of the island, where he rules over his tribe of savages. Jack becomes a ruthless, tyrannical leader, who punishes his enemies and spreads false rumors regarding the beast. Jack leads his tribe on violent, exciting hunts and establishes his headquarters at Castle Rock. He then conducts two raids on Ralph's camp and threatens to harm anyone associating with him. Towards the end of the novel, Jack views himself as the unquestionable leader and commands his tribe to hunt Ralph. Essentially, Jack changes from being a civilized, albeit obnoxious child to a ruthless savage.

In Lord of the Flies, Jack's character morphs from that of civilized choir boy to savage hunter.  At the beginning of the novel, Golding emphasizes Jack's clothing as defining his role as a leader.  Jack Merridew's body "from throat to ankle" is concealed by a black cloak with a "long silver cross on the left breast;" his golden cap badge denotes him as being a leader among the other choir boys (21).  Jack's status as head choir boy gives him authority and power over the other boys:

"'I ought to be chief,' said Jack with simple arrogance, 'because I'm chapter chorister and head boy. I can sing C sharp'" (22).

As his time on the island lengthens, Jack desires to maintain the feeling of authority and power that he enjoyed from his head boy position and replaces that civilized role with the role of being the best hunter.  From the very first tribal meeting, Jack made it clear among the other boys that he wishes to be chief, and he uses his influence as the best hunter in an attempt to supplant the boys' chosen leader, Ralph.  The scene in chapter four in which Jack paints a mask onto his face reveals much about his transformation from choir boy to savage:

"He looked in astonishment, no longer at himself but an awesome stranger. [...] He began to dance and his laughter became a bloodthirsty snarling" (64).

Hunting and the creation of the mask serves as a catalyst for Jack's descent into savagery on the island.  He goes from being a boy who could not stand the idea of blood, to one who relishes the kill.  Furthermore, wearing the mask "liberated" Jack from "shame and self-consciousness" (64).  By the end of the novel, Jack behaves as a true blood-thirsty savage, willing to kill any of those who would challenge his power.

In Lord of the Flies by William Golding, how has Jack's appearance changed by the last chapter?

When Jack first appears in Lord of the Flies in Chapter 1, he is dressed like a choir boy in a robe and black cap. Jack is the model of decorum, and he feels like he should be the leader. He is described as freckled, bony, and ugly, and he has bright red hair, symbolic of the blood he will later thirst for. He quickly discards his robe and grabs a knife in a sheath. Jack eventually also discards his shoes, and he goes about with bare feet.

By Chapter 2, he becomes dirty, as he chases wild piglets on the island and tries to slaughter them, and he is covered with dirt and blood. He is often carrying the knife or a long spear about with him. Jack covers his face with colored chalk that he finds on the island. He is the image of savagery, and he has already forgotten about the prospect of being rescued. 

In Lord of the Flies by William Golding, how has Jack's appearance changed by the last chapter?

Jack's appearance changes in interesting ways throughout Lord of the Flies. The first time Jack experiments with wearing paint is in chapter 4. After that, he wears some paint when he hunts. Even in chapter 7, however, Jack continues to look like the other boys. As Ralph watches the hunters eating, he notices the state of their clothes. All of them still wear their clothes, even though they are "put on, not for decorum or comfort but out of custom." In chapter 8, however, Jack tries to lead a rebellion against Ralph and calls for a vote to remove Ralph as chief. When that vote doesn't go his way, he decides he is "not going to play any longer. Not with you." He then leaves Ralph's group and establishes his own tribe with his hunters, the boys who were originally part of the choir, who still wear their choir caps. After they kill a pig, they realize they have no way to cook it since Ralph's group has the fire and the means of starting it. Jack decides they will steal some fire. In preparation for that confrontation, they put on paint. 

During the surprise visit, "demoniac figures with faces of white and red and green rushed out howling." While two boys steal fire, Jack and two others remain to talk to Ralph's group. Jack is "stark naked save for paint and a belt." 

In chapter 9, at Jack's feast, he is "painted and garlanded" as he sits on the log that serves as his throne. In chapter 10, when Jack's tribe has moved to Castle Rock, Jack is described as "naked to the waist, his face blocked out in white and red." At the end of the book, Jack appears before the naval officer as "a little boy who wore the remains of an extraordinary black cap on his red hair and who carried the remains of a pair of spectacles at his waist."

Jack's changing appearance throughout the novel tracks his descent into savagery as well as his claim to leadership and power. 

In Lord of the Flies by William Golding, how has Jack's appearance changed by the last chapter?

By the end of the novel, Jack has adopted a mask to hide behind. He paints his face and has become one with the "kill or be killed environment" in which he lives. He reminds one of remote tribes where superstition and death reign supreme. The mask allows Jack to abandon the civilized world of which he was a part. When he paints his face, he is no longer Jack. He is the hunter, the tribal leader, the killer of pigs and other things. The mask allows him the freedom to be his id.

In William Golding's Lord of the Flies, how does Jack's character change from the beginning of the novel to the end?

We meet Jack Merridew in the first chapter of William Golding's Lord of the Flies, as he leads his choir toward the sound of the conch. The characteristics he displays then are the same characteristics he demonstrates at the end of the novel; his cruel nature is simply magnified and intensified as the story progresses. 

Jack is effective in keeping his choir under control, but he does so through intimidation. The fully robed boys follow Jack to the meeting place on the beach. "When his party was about ten yards from the platform he shouted an order and they halted, gasping, sweating, swaying in the fierce light." Despite the boys' obvious discomfort, Jack orders them to "halt" but does not let them sit or take off their sweltering clothes until they beg him.

Golding describes Jack this way:

he was tall, thin, and bony; and his hair was red beneath the black cap. His face was crumpled and freckled, and ugly without silliness. Out of this face stared two light blue eyes, frustrated now, and turning, or ready to turn, to anger.

Immediately Jack demands to know who is in charge, and from the beginning, Jack taunts Piggy and calls him names, simply because of Piggy's physical appearance. He is an angry, frustrated boy. The group decides to elect a leader.

“I ought to be chief,” said Jack with simple arrogance, “because I’m chapter chorister and head boy. I can sing C sharp.”

When Ralph asks who wants to vote for Jack, no one responds immediately--not even the choirboys until "with dreary obedience the choir raised their hands." When Ralph wins this election, Jack is embarrassed, but Ralph appeases him by telling Jack he can have the choir as hunters.

Jack likes to explore, but he particularly likes to hunt. He is obsessed with hunting--the only thing which is important to him--and does nothing to make himself useful around the camp. While Ralph wants shelter, Jack wants meat. 

The moment when Jack begins to transform in a significant way is when he begins painting his face to hunt. Something happens which turns Jack from a surly boy with a knife into a "savage." After he paints his face, he looks at his reflection in some water.

He looked in astonishment, no longer at himself but at an awesome stranger. He spilt the water and leapt to his feet, laughing excitedly. Beside the pool his sinewy body held up a mask that drew their eyes and appalled them. He began to dance and his laughter became a bloodthirsty snarling.... [T]he mask was a thing on its own, behind which Jack hid, liberated from shame and self-consciousness. 

Jack, like the others, has had no adult authority on the island; however, until now he has demonstrated the self-restraint of his conscience to keep from doing anything truly awful (though Piggy has known almost from the beginning that Jack would like to get rid of both Piggy and Ralph). Now, behind the mask, Jack has nothing to restrain him, and this is the beginning of his descent into savagery.

By the end of the novel, Jack is a leader again; he is the chief of a tribe of savages. He maintains control of the boys by threatening and intimidating them. Once Piggy and Simon are dead, the only impediment to Jack's complete control of the island based on his own self-centered, evil human nature is Ralph. When Jack orders his tribe to kill Ralph, no one doubts that he means it, including Ralph. Jack's tribe follows his orders, just as his choir did in the beginning. 

In William Golding's Lord of the Flies, how does Jack change after he was not elected chief in the first chapter?

Lord of the Flies, by William Golding, recounts the story of some English schoolboys who have been stranded on a tropical island after their airplane crashed. Most of them do not know one another; the exception is a group of choirboys of whom Jack Merridew is the leader.

Jack and the other choirboys come marching across the beach after hearing Ralph blow the conch shell. It is clear from the beginning that Jack is a strict leader, because they all remain standing, despite the heat and their fatigue, until he allows them to sit. Eventually the entire group decides to vote for a leader. Ralph is the first to suggest it and the others begin clamoring for a chief. Jack, of course, assumes he is the obvious choice because he is already a leader.

“I ought to be chief,” said Jack with simple arrogance, “because I’m chapter chorister and head boy. I can sing C sharp.”

What we soon deduce is that Jack is not an effective leader, as evidenced by the fact that none of his choirboys want to vote for him but are pressured by his look into doing so. (And of course being able to sing a C sharp is not a useful skill in these circumstances.)

After Ralph wins the simple election, 

...the circle of boys broke into applause. Even the choir applauded; and the freckles on Jack’s face disappeared under a blush of mortification. He started up, then changed his mind and sat down again while the air rang.

In an attempt at appeasement, Ralph offers Jack the chance to be leader of his choirboys and choose what they will do; Jack chooses hunting and thus becomes the leader of the hunters. Hunting soon becomes an obsession for Jack, and eventually he paints his face and evolves into the chief savage on the island. He does not recognize Ralph's authority and he is consumed with a desire to kill.

It is interesting to wonder how things might have been different if Jack had won that election; however, given his history as an ineffective leader, it is likely the boys' descent into savagery might have happened even more quickly if Jack had been the leader.