how is jack presented to the reader?

Jack is an antagonist. He has leadership qualities in a dictatorial sort of way. He has a lot of control and self-esteem issues. When we first meet him he is constantly stabbing trees in a show of toughness to the other boys. Jack feeds off of fear. He goes after Piggy from the start because Piggy is weak. Golding describes Jack as "ugly without silliness". He is a boy that speaks his mind and turns to violence when he does not get his way. These are the seeds of Jack evolving into the crazy demi-god/king that he makes himself into by the end of the book.