Who is Geoffrey from This Boy's Life and what is their importance?

Geoffrey is Toby's older brother. At the beginning of the book, Geoffrey lives on the east coast with his father and his father's new wife. He doesn't have any contact with Toby until he goes to Princeton and starts sending Toby letters and stories. Initially it seems like Geoffrey's got it pretty easy, but it becomes clear that he's gone through some difficult times with his father.