In my opinion, I believe that Jack has changed the most significantly throughout the course of the book. From respectable to savage and from responsible Head Boy to corrupt leader.
At the start of the book Jack was in command of his choir and he had them in columns of two, and even had them marching. He was also very bossy and he shouted orders at them, "he shouted an order and they halted". Since they followed his order as soon as he called it, it shows that they were used to obeying Jack. This also shows that he demanded respect from everyone, even his class mates. He keeps this attitude throughout the book. He is the leader of the choir and they become the hunters (that kill). This would lead to Jack being associated with evil and death. He seems to harbour emotions of anger and savagery.
Jack has been described in the book as being, "...thin
and bony; and his hair was red...". At a later stage of the book he would be likely described as having dirty hair. He has also been described as being "ugly without silliness". This would show that he would not have a sense of humour and would be very serious.
He used to be civilised and this is shown when he said with pride when they were picking their leader, "... I'm Head Boy". Since he was Head Boy, it would lead you to believe that he was respected by teachers. Being Head Boy he would have had to enforce the rules at school and give out punishments if the pupils repeatedly broke the rules, but turns against all of his old beliefs by the end of the book.
He thinks that the boys are not savages because they are English and...