Rex Koury was born in London, England in 1911, though his parents came to America the next year, settling in New Jersey. In 1924, he attended his first movie and was more captivated by the pipe organ accompaniment than by the movie itself. He immediately decided to become an organist.
Koury convinced the organist of the local Cranford Theatre to allow him to play the movie trailers for free, and he was so successful that his duties were quickly increased. He held cinema organ positions at several theaters, including a contract with RKO Proctor's Fourth Street Theatre in Troy where he was billed by the theatre as "The Youngest Professional Organist in America." In 1933, as the cinema organ industry was starting to wind down, he moved to Hollywood and worked as a conductor, pianist, and composer for movie studios. Koury did continue to perform as an organist in concert and for the radio; during World War II, he was solo organist for several military radio programs. During his decades in Hollywood, Koury held music director positions with several studios and composed and directed the music for numerous shows. His most famous Hollywood composition was the Western‑style theme for Gunsmoke, originally a radio program that later became the long‑running television show. Koury wrote many organ solos and organ & piano duets for Lorenz Publishing Co. throughout his career. He died in Wyoming in 2006 at the age of ninety‑five.