Ralph R. Greenson (born Romeo Samuel Greenschpoon, September 20, 1911 – November 24, 1979) was a prominent American psychiatrist and psychoanalyst. Greenson provided psychiatric care to Marilyn Monroe. He was the inspiration for Leo Rosten's 1963 novel, Captain Newman, M.D.. The book was later made into a movie starring Gregory Peck as Greenson's character.