His experiences at the school taught him to develop a detached, analytical style considered cold by all but his closest friends,[7] though he could, like his father,[4] be disarming and funny in social situations.

[11] During World War II, de Camp served as a researcher at the Philadelphia Naval Yard along with his fellow writers Isaac Asimov and Robert A. Heinlein.

[12] De Camp was a member of the all-male literary and dining club the "Trap Door Spiders" in New York City, which served as the basis of Asimov's fictional group of mystery solvers the "Black Widowers."

The collection included books inscribed by fellow writers, such as Isaac Asimov and Carl Sagan, as well as de Camp himself.

In 2019 de Camp's theory was scientifically tested by C. G. M. Paxton and D. Naish, who concluded that trends in the data of reported sightings appear to support his hypothesis.

For example, in the Harold Shea stories co-written with his longtime friend Fletcher Pratt (1897–1956), the magical premises of some bodies of myths and legends were accepted but examined and elucidated in terms of their own systems of inherent logic.

[19] De Camp's explanatory tendency also carried over into his non-fictional writings, including advice to science fiction writers on handling the different states of languages in future worlds.

[8] De Camp eschewed the intention of being a satirist, insisting, instead, that the stories he wrote were meant less for instruction or improvement, as satire requires, and more for the amusement of his readers.

Instead, de Camp, through sound background knowledge and logical thought, systematically demonstrated how technological advances could determine the pattern of an eventful history.

[24] He was also known for his sword and sorcery, a fantasy genre revived partly by his editorial work on and continuation of Robert E. Howard's Conan cycle.

The Pusadian series (from 1951), composed of the novel The Tritonian Ring and several short stories, is set in an antediluvian era similar to Howard's.

Other novels in the sequence include The Fallible Fiend, a satire told from the point of view of a demon, and The Honorable Barbarian, a follow-up to the trilogy featuring Jorian's brother as the hero.

The sequence is set in the medieval era of another alternate world sharing the geography of our own, but in which a Neapolitan empire filled the role of Rome and no universal religion like Christianity ever arose, leaving its nations split among competing pagan sects.

De Camp also wrote historical fiction set in the era of classical antiquity from the height of the First Persian Empire to the waning of the Hellenistic period.

Five novels published by Doubleday from 1958 to 1969[1] form a loosely connected series based on their common setting and occasional cross references.

They were also linked by a common focus on the advancement of scientific knowledge, de Camp's chosen protagonists being explorers, artisans, engineers, innovators and practical philosophers rather than famous names from antiquity, who are relegated to secondary roles.

He conducted extensive research for what was to be a book on magic, witchcraft and occultism, though only the first chapter, "The Unwritten Classics" (March 1947), was published in the Saturday Review of Literature.

[7] By May 1976, concerned with what Paul Kurtz described as "an enormous increase in public interest in psychic phenomena, the occult and pseudoscience," de Camp joined the newly formed Committee for the Scientific Investigation of Claims of the Paranormal along with astronomers George Abell, Bart Bok, and Carl Sagan; philosophers Brand Blanshard, Antony Flew, Sidney Hook, and Ernest Nagel; authors Isaac Asimov, Daniel Cohen, Charles Fair, Martin Gardner, and Phillip J. Klass; psychologists Ray Hyman and B.F Skinner; and magician James Randi.

Some others of his many and wide-ranging nonfiction works were The Great Monkey Trial (about the Scopes Trial), The Ragged Edge of Science, Energy and Power, The Heroic Age of American Invention, The Day of the Dinosaur (which argued, among other things, that evolution took hold after Darwin because of the Victorian interest spurred by recently popularized dinosaur remains, corresponding to legends of dragons), Great Cities of the Ancient World and The Evolution of Naval Weapons (a United States government textbook).

[36] De Camp and Willy Ley won the 1953 International Fantasy Award for nonfiction recognizing their study of geographical myths, Lands Beyond (Rinehart, 1952).

Randall Garrett conflated him with J. R. R. Tolkien's Gandalf in the character of the magician "Sir Lyon Gandolphus Gray" in his Lord Darcy series.

He was the model for the "Geoffrey Avalon" character in Isaac Asimov's fictional group of mystery solvers the "Black Widowers,"[13] and the unnamed court magician in Lawrence Watt-Evans' "Return to Xanadu" (The Enchanter Completed: A Tribute Anthology for L. Sprague de Camp, 2005).

He also appears without fictional disguise in the short stories "Green Fire" by Eileen Gunn, Andy Duncan, Pat Murphy, and Michael Swanwick (Asimov's Science Fiction, April 2000) and "Father Figures" by Susan Shwartz (The Enchanter Completed: A Tribute Anthology for L. Sprague de Camp, 2005),[41] and in the novels In the Courts of the Crimson Kings (2008) by S. M. Stirling and The Astounding, the Amazing, and the Unknown (2011) by Paul Malmont.

De Camp's name does not specifically appear in the episode credits, which identify the roles of actors in the scene as composite characters.