Who is The Narrator from The Sorrow of War: A Novel of North Vietnam and what is their importance?

In the book's conclusion, we learn that the narrator is Kien's neighbor. This individual took on the task of putting Kien's writings into narrative form. The narrator also reveals that he is a fellow soldier and has much in common with Kien, giving the reader the sense that in making sense of Kien's life, he is also able to make sense of his own.