In the late 1950s, collaborating with countryman Claude Moliterni [fr] (later the editorial director of the French publisher Dargaud) under the joint pen names Karl von Kraft and Franck Sauvage (after Doc Savage),[3] Horn co-wrote a number of French-language pulp mystery and spy novels.
[3] Returning frequently to France, he was a member of the 1960s groups Club Bande Dessinée and SOCERLID ("Société civile d’études et de recherché des littératures dessinées"), which championed the idea of comics as "the ninth art" and worthy of academic study.
[9] The World Encyclopedia of Cartoons (first published in 1979) profiles the lives and work of more than 1,5000 cartoonists and animators from the United States, Europe, Russia, Japan, and South America.
His dictionary-style reference book Contemporary Graphic Artists (1986) included designers as well as illustrators, animators, and cartoonists, and highlighted each entrant's most famous works.
Milton Caniff styled the Steve Canyon character M’sieu Toute (appearing in July through September 1968) after Horn.