As superhero comics waned in popularity after the end of World War II, Simon & Kirby producing a variety of other genre stories. In partnership with Crestwood Publications a.k.a. Prize Comics, they launched an early horror, the atmospheric and non-gory Black Magic, and others. Simon & Kirby are credited as well with publishing the first romance title, Young Romance Comics. In addition, Kirby and Simon produced crime, and humor comics.
1974 Comic Art Convention program, reprinting Simon's original 1940 sketch of Captain America.
Later, in 1953, they would form their own short-lived comics company, Mainline Publications, creating the masked Western hero Bullseye, the superhero-parody character Fighting American, and others.
The partnership ended in 1955 with the comic book industry beset by self-imposed censorship, negative publicity, and a slump in sales. Simon turned primarily to advertising and commercial art, while dipping back into comics on occasion.