The "Lord of the Flies," or the beast, inhabits the severed pig head that Jack's hunters stake into the ground and leave as an offering. Simon recognizes that the Lord of the Flies is the savage monster buried in everyone. When the Lord of Flies tells Simon "we are going to have fun on this island," it means they're going to indulge every want and desire, without regard to the rules of civilization. The name "Lord of the Flies" is a reference to the name of the Biblical devil Beelzebub, so on one level, "the beast" is a kind of savage supernatural figure, but mostly it symbolizes the evil and violence that potentially exists in the heart of every human.