Who is Johnny Merrimon from The Last Child and what is their importance?

Johnny Merrimon is the main character and protagonist in the novel, The Last Child. He is a heroic young man, who has had a tough life. Johnny has become his mother's 'de facto' caretaker, as she slides deeper into her addiction. He misses his father. and he deeply resents and fears Ken Holloway (his mother's boyfriend and source of drugs).