Who is Riley Henderson from The Grass Harp and what is their importance?

Riley Henderson is the young man who lives in the tree house temporarily during Dolly's rebellion. He is a friend of Collin's, but he has much more worldly experience. Riley's father died when he was a boy, and his and mother is in a mental institution. Thus, Riley has been left not only just to care for himself his two younger sisters as well. After the tree house episode, Riley matures, marries and becomes a businessman in the town.