Jack uses the beast to create an atmosphere of hysteria and manipulate the boys' fears in order to control them. Jack portrays himself as the ultimate hunter and fearless leader of his tribe. As the most successful hunter of the group, Jack plays the role of protector and guardian. Although Ralph is still the elected chief, Jack uses the beast to bolster his popularity and elevate his status among the group.
The majority of the boys believe that Jack can protect them from the beast and willingly follow his lead. Ralph cannot compete with Jack's role as guardian and provider, which allows Jack to easily usurp power. Many of the boys leave Ralph's group to join Jack's tribe of savages at the opposite end of the island, where chaos reigns supreme.
Jack does not deny the beast's existence, because he understands how fear affects the boys. He brilliantly contributes to the hysteria surrounding the beast by leaving a severed pig's head behind as an offering and leading an expedition in search of the mysterious creature. The boys subscribe to his theory regarding the beast and obediently follow his directives without question.
After the boys brutally murder Simon, Jack tells his hunters that the beast is still alive and says that the creature disguised itself on the beach. Jack then comments,
He [the beast] may come again even though we gave him the head of our kill to eat. So watch; and be careful...I expect the beast disguised itself...We'd better keep on the right side of him, anyhow. You can’t tell what he might do.
Jack knowingly uses the beast as a scare tactic to arouse fear amongst the group. The hysterical boys do not think rationally, allowing Jack to control them and make every decision. Essentially, Jack coerces the boys into following his directives by creating a hysterical environment and portraying himself as their only protector.