Who is Du Thien from Jasmine and what is their importance?

Du Thien was Jasmine and Bud's adopted son. He was Vietnamese and came from a large family in Saigon. As a survivor of a refugee camp, Du and Jasmine share memories of torture, violence and a fight for life. He was adopted at the age of fourteen. At the end of the novel, Du is leaving Iowa to search for his only living relation..... his sister.