To add to what the other editors have said, you might mention that Jack is hedonistic. He lives in the here and now. His mantra is "We'll have fun on this island." He has no use for long-term goals of rescue or shelter. Instead he enjoys the thrill of the hunt and resents anyone who stands in his way of his savage-like pursuits. He continues to roll rocks when Ralph has clearly abandoned such pastimes. When he is not not elected chief in the second election, Jack declares that he doesn't want to play anymore. Jack cannot get past the fact that the survival on the island is more than fun and games. He operates solely on the principle of pleasure/pain. What brings pleasure to him is good; what brings pain to him is bad.
In the book The Lord of the Flies Jack is a very dominating person. He tries to take over as the leader and he succeeds.
Jack is animalistic as he is willing to shed blood and does not care if it hurts someone or something.
Jack is intimidating. It is difficult for the other boys to stand up to Jack because they don't know what bad thing he would do to them.
Jack is egotistic. Jack demonstrates the need to have power over others. He seats himself as if he is a king on a throne and gives orders to others. The power is what he craves and the control.
Jack is the essence of what man could become without laws and guidance. He is man at his rawest level.
In the novel LORD OF THE FLIES, Jack is the character that experiences the most changes of anyone throughout the story. He is systematic and regimented believing in structure and order, "We've got to have rules and obey them. After all, we're not savages. We're English, and the English are the best at everything. So we've got to do the right things." (p.42) As the story continues, Jack becomes very hostile and arrogant believing he is right and knows what is best for everyone. Jack is an interesting example of the "innocent" who becomes corrupted and tainted by power, a frequently seen archetype in literature.