Jack Merridew is the leader of the boys’ choir, and later the hunters, and Ralph’s competitor for leadership on the island.
Jack Merridew is a natural leader. He actually has leadership experience, unlike Ralph. He has been the choir leader at his school, and he seems to take responsibility over the choir even after they crash land on the island. This is because Jack loves power, and he is not willing to give it up just because they are not in school.
Jack takes everything seriously. He wants control and power. Even the physical description of him seems to reinforce these characteristics.
Inside the floating cloak 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. (Ch. 1)
Jack is mercurial. When Ralph is chosen leader, he accepts it more easily than you would think. This is because he seems to know that he will be able to challenge Ralph eventually. The conch gave Ralph leadership, but Jack’s abilities are innate.
“The choir belongs to you, of course.”
“They could be the army—”
“They could be—”
The suffusion drained away from Jack’s face. Ralph waved again for silence.
“Jack’s in charge of the choir. They can be—what do you want them to be?”
“Hunters.” (Ch. 1)
As leader of the hunters, Jack is eventually successful in getting meat. The allure of savagery leads the other boys to join him. Jack represents the much more attractive aspects of killing and dancing with war paint. As leader, he does not try to institute democracy and order like Ralph. His is a dictatorial regime. He does things like tie kids to trees and have them beaten.
In the end, it is the chaos that Jack causes when he breaks up the group and his propensity to savagery that leads to the deaths of Piggy and Simon. Ralph knows this, and he blames himself because he could not maintain leadership. By giving in to Jack, he doomed them all.