After attending art school and working as a parking valet and other odd jobs for nightclubs, Mooney went to New York City in 1940 to enter the fledgling comic-book field. Following his first assignment, the new feature "The Moth" in Fox Publications' "Mystery Men Comics" #9–12 (April–July 1940), Mooney worked for the comic-book packager Eisner & Iger, one of the studios that would supply outsourced comics to publishers testing the waters of the new medium. He left voluntarily after two weeks: "I was just absolutely crestfallen when I looked at some of the guys’ work. Lou Fine was working there, Nick Cardy ... and Eisner himself. I was beginning to feel that I was way, way in beyond my depth..."