In chapter 5, Jack cries:

“Bollocks to the rules! We’re strong—we hunt! If there’s a beast, we’ll hunt it down! We’ll close in and beat and beat and beat—!”

This bold assertion of violence excites the listening boys, and they respond approvingly, "full of noise and excitement, scramblings, screams and laughter."

When the novel opens, choir leader Jack is angry and sulky because he is not elected leader. At that point though he shows a willingness to follow civilized rules and norms. As time goes on he realizes that giving into his lust for violence and rule-breaking is a potent source of power. He can gain followers and do what he wants the more savage and autocratic his behavior becomes. He recognizes that in the absence of adult authority, there is no one to put a stop to his violence.

Jack, the Hitler figure in the novel, abandons logic, reason, and the rule of law. Instead, he appeals to the most atavistic, "primitive" desires in the boys and encourages them to let their ids run loose. His society of hunting, violent ritual, cruelty, sadism, wild dancing, and body painting is so alluring it wins out over Ralph and Piggy's less entrancing world of rationality, foresight, and decency. Left to their own devices, the boys simply follow the one who allows them to give into the impulses of the moment.

By the end of the novel Jack's leadership set the island on fire, which, ironically, catches the attention of the British ship that comes to rescue them.

In Lord of the Flies, Jack is disappointed and surprised that he is not the natural choice for leader and, instead, the boys, stranded on a deserted island, vote for Ralph as chief. It is something of a consolation that Jack, as "chapter chorister" of a group of some of the boys will be in charge of, as he calls them, the "hunters." Jack does have a respect for Ralph, at first, although he does regularly challenge authority. Determined to catch a pig, Jack wants to camouflage himself which disguise gives him an exhilarated feeling to the point where his laughter is described as "a bloodthirsty snarling." The reader is told that,"Jack hid, liberated from shame and self-consciousness," (ch 4). The reader is thus forewarned and is being prepared for what may follow as Jack continues to show signs of what lengths he will go to in order to exert his authority. 

Piggy is afraid of Jack, who bullies and makes fun of him. In chapter 5, Piggy who is insightful and intelligent tells Ralph that he is scared of Jack:

If you're scared of someone you hate him but you can't stop thinking about him. You kid yourself that he's all right really, an' then when you see him again; it's like asthma an' you can't breathe. I tell you what. He hates you too, Ralph-"

As the plot unfolds, Piggy's words prove to be correct and it is Jack's ability to lead by fear that allows him to form his "tribe." Jack has his tribe chanting "Kill the beast! Cut his throat! Spill his blood!" This is the same chant which has the tribe in such a frenzy that they kill Simon without recognizing him.

In chapter 11,Piggy will suffer a similar fate at Jack's hands but, before this, Jack seizes an opportunity to capture Samenric, shouting angrily at his tribe to "grab them!" It is obvious that they are operating on Jack's orders:

The painted group moved round Samneric nervously and unhandily...."Tie them up!"...Now the group... felt the power in thier hands...Jack was inspired..."See? They do what I want."

Jack is proud of his "solid mass of menace," and before long, more tragedy strikes as Piggy is catapulted through the air. He is dead but Jack can only relish his position as the obvious "Chief," when he says "See? See? That's what you'll get! I meant that!"  

Simon and Piggy are both dead and Ralph's life is in danger. Ralph, especially as he realizes that he will be unable to persuade Samenric to help him create an "outlaw" tribe against Jack, can only hide away now as Jack seems to become more powerful as he becomes more savage.    

In chapter 8, Jack makes the others tie Wilfred up for apparently no reason, and beats him.

Jack rules by violence, not democracy.  He makes decisions out of anger, and enforces them by fear.  For example, he gets mad and has Wilfred tied up for hours, waiting to be beaten for some unnamed crime.

The chief was sitting there, naked to the waist, his face blocked out in white and red. The tribe lay in a semicircle before him. The newly beaten and untied Wilfred was sniffing noisily in the background. (ch 8)

The other boys, especially the hunters at first, respond to Jack’s violence.  He makes everything seem exciting.  He has experience in leadership as head of the choir, but even then he was a drill sergeant, leading by bullying.

Even when he is not attacking the pig or beating up boys, Jack is impulsive and violent.  He acts without thinking, and yells and pouts.  He rages and tantrums, and the other boys learn to see him as volatile and dangerous.