Who is Nathan from American Pastoral and what is their importance?

In the beginning of the story, when Nathan Zuckerman is at his high school reunion, Jerry arrives and tells him the basics of Swede's life story, telling him that Swede has died. Nathan is an author and, supposedly, goes on to fill in the story of the Levovs. Nathan was a friend of Jerry Levov's, who played ping-pong with him when they were children. But his greatest hope was to be acknowledged by Jerry's brother, the heroic athlete Swede Levov.