D.B. Caulfield is Holden Caulfield's older brother in The Catcher in the Rye. Holden considers D.B. to be his favorite writer due to the fact that he used to write fantastic short stories, but believes that D.B. is a "phony" for "selling out" and becoming a very successful screenwriter in Hollywood rather than a "real" writer.
It is also worth noting that D.B. served in the Army for four years and fought in World War II before becoming a screenwriter. He despised this experience, especially because he was so young when he enlisted, stating that "the Army was practically as full of bastards as the Nazis were." Although Allie (the boys' brother who later died of cancer at the age of eleven) wonders if D.B.'s participation in the war made him into a better writer and provided him with more material to write about, D.B. knows that this experience ultimately didn't serve his artistry and instead traumatized him.
Holden's brother D.B. is in Hollywood, California, he writes for the movies. Holden does not respect his brother because he believes that he should be writing serious things, like books.
So, D.B., the Hollywood scriptwriter is just another phony in Holden's life.