Born and raised in Belgium, Morris moved to the United States in 1946 for six years. There, he worked for MAD magazine and met Rene Goscinny. After Goscinny's death, several other writers contributed to "Lucky Luke," including Bob de Groot, the well-known writer of such very successful humorous series as "Robin Dubois," "Leonard" and "Clifton," the latter published in English by Cinebook.