Jerome Kern (1885-1945) composed the music for Show Boat (1927), one of the first true musicals of Broadway, and one of the first musicals translated to the big screen (1936). The show's most famous song, Old Man River, was sung by Paul Robeson.
Irving Berlin (1888-1989) was a mature songwriter by the time sound was added to motion pictures, so he naturally became one of the first composers for films. He also wrote the lyrics for many of his songs. His film musicals include hits such as Top Hat, Easter Parade and Holiday Inn, which features one of his biggest hits, White Christmas.
Harold Arlen (1905-1986), the son of a cantor, was the genius behind the music for The Wizard of Oz and seven of the songs for A Star is Born (1954), also with Judy Garland.
Leonard Bernstein (1918-1990) is known primarily for his years conducting the New York Philharmonic Orchestra, but he also composed the music for one of the most iconic stories of Broadway and film, West Side Story.
Alan Menken composed the music for some of Disney's most recent films as well as several others. His hits include Sister Act and Little Shop of Horrors (also for Broadway) and for Disney: Aladdin, Pocahontas, The Hunchback of Notre Dame, and Beauty and the Beast.