His parents were actors, Bennett Kilburn Mercer and Nola Margaret Miller (stage name Nola St. Claire), but Jack decided to pursue his love of art. He got a job as an inbetweener (rookie animator) at the Fleischer studio. Dave Fleischer happened to hear him singing the Popeye theme song in a funny voice, and asked Jack to try voicing one cartoon. He later became a writer at the Fleischer studio.