During the 1920s, sound revolutionized the motion picture industry and cinema continued as one of the most significant and popular forms of mass entertainment in the world. Film studios were transformed into major corporations, hiring a host of craftsmen and technicians including cinematographers, editors, screenwriters, and set designers. The birth of the star system supported the meteoric rise and celebrity status of actors including Charlie Chaplin, Mary Pickford, Joan Crawford, Greta Garbo, and Rudolph Valentino while black performers (relegated to "race films") appeared infrequently in mainstream movies. The classic Hollywood film style was perfected and significant film genres were established: the melodrama, western, historical epic, and romantic comedy, along with slapstick, science fiction, and fantasy. In ten original essays, American Cinema of the 1920s examines the film industry's continued growth and prosperity while focusing on important themes of the era.