in what ways do we come to know that jack is the antagonist of the story?

Jack begins the story as the autocratic leader of the choir. He does not want to be called by his first name rather than his sir name. He wants to be called "Merridew" to stand out; he wants to assert his dominance. When Ralph gets the popular vote for leader, Jack is mortified. Although Ralph appeases him with his hunters, Jack forever becomes antagonist to Ralph. Jack undermines Ralph's authority at every turn. He accuses Ralph of favouring Piggy, the boy who is constantly mocked. He maintains that Ralph is afraid of the beast where as he will kill it. Finally Jack openly forces a change in leadership. After his tirade, "I shan’t play anymore", he slinks off into the jungle. One by one most of the boys accept Jack's assertion of Ralph's weakness and boring responsibility. In the end Jack strips Ralph of all his power. If it was not for the sailor showing up Jack would most certainly have taken Ralph's life.