Who is David Patchen from The Tears of Autumn and what is their importance?

Paul Christopher's oldest and best friend in the Agency, David is the fourth highest administrator. He and Paul meet as patients in a naval hospital at the end of World War II. They are roommates at Harvard and are recruited together. Because of his wounds, which make him easily identifiable, David goes into administration, at which his photographic memory makes him brilliant, while Paul goes into the field. When they first meet in the novel, in a safe house on Q Street, Washington, DC, David fears Paul wants to quit the Agency and that his girlfriend Molly will not be enough for him. David observes that the Kennedy Administration is filled with innocents who have never smelled a corpse and do not understand consequences.