John D. Clark (1907-1988) was a noted American chemist and science fiction writer and fan. He received his Ph.D. from Stanford in 1934. From 1949 to 1970 he was the Chief Chemist at the Naval Air Rocket Test Station in Dover, New Jersey, which later became the Liquid Rocket Propulsion Laboratory of Picatinny Arsenal, where he developed liquid propellants. In 1972 he published a nonfiction work, Ignition! An Informal History of Liquid Rocket Propellants which included a preface by his friend, Isaac Asimov.

Clark was an active member of the early science fiction community. He published several stories in the 1930s with his friend L. Sprague de Camp and was friendly with other notable figures including L. Ron Hubbard and Fletcher Pratt. He became a fan of Robert E. Howard's fantasy stories in the 1930s. With P. Schuyler Miller, Clark worked out an outline of Conan's career as well as a map of his world, which he sent to Howard, who confirmed and corrected their findings, which were eventually published in the 1938 fanzine The Hyborian Age. Recognized as an early authority on Howard's work, Clark was invited to write introductions to the Gnome Press collections of his work in the 1950s. The Archive contains the materials relating to the publication and revisions of these items.