Wendy, Marvin and Wonder Dog were first introduced in DC Comics with the January 1976 tabloid comic "Limited Collectors' Edition presents: Super Friends" #C-41, in which the newcomers are welcomed to the Hall of Justice to meet the entire Justice League of America, including characters who didn't appear on the show. Their story was mostly a frame to bookend reprints of older "Justice League" comics, but each character got their own spotlight. Superman tells Wonder Dog about Krypto, the Dog of Steel, to reassure him (and the readers) that there's a precedent for canine superheroes adventuring with the Justice League.