Jack (and his tribe) represent anarchy. Jack did not have the integrity to keep the Beast at bay. He is the perpetrator of all three deaths that occur on the island and wishes to spend his time hunting (killing) instead of helping Ralph with rescue.
Jack Merridew is a young boy, probably the same age as Ralph, possibly older. On pg. 20 Golding describes Jack as tall, thin and bony; and his hair was red beneath the black cap. His face was crumpled and freckled, and ugly without silliness. Out of this face stared two light blue eyes, frustrated now, and turning, or ready to turn, to anger.
Jacks eyes are always used in the novel to depict his emotions, as they are in the quote above. When the boys land on the island they are all wearing their school uniforms, but Jack and his choir are wearing cloaks and caps. Jack is one of the only boys whose last name is learned. I think the author does this to make Jack stand out. He is a very important character because throughout this whole novel, Golding depicts this island and savagery to everyday life.