The Nyctalope, also known as Léon "Leo" Saint-Clair, is a pulp fiction hero and explorer created in 1911 by French writer Jean de La Hire. Along with being an athletic man with great wealth and strong scientific knowledge, the Saint-Clair has perfect night vision and enhanced eyesight due to a gunshot wound affecting his optic nerves in a unique way.L'Assassinat du Nyctalope ("The Assassination of the Nyctalope") (1933). Enter the Nyctalope, as translated by Brian Stableford and published by Black Coat Press (). This, and the side-effect that his eyes now sometimes have a yellow, reflective coloring, inspires his nickname "Nyctalope" (which, in French, refers to an animal with excellent night vision, although in English the same word refers to night-blindness). Due to an experimental surgery, the Nyctalope also possesses a mechanical, electrical heart that increases his vitality and stamina. Because he has an artificial organ that grants enhanced abilities, some consider the Nyctalope to be the first adventurer in literature who is also a cyborg.

Largely unknown outside of France during the 20th century, the character is now considered by some to be an obscure precursor to the superhero genre. Most Nyctalope storylines were presented in serialized form in French publications, then quickly collected and republished as novels. In 1908, author La Hire wrote the story L'Homme Qui Peut Vivre dans l'Eau (in English, "The Man Who Could Live Underwater"). In it, a support character named Jean Sainte-Claire aids the protagonist. In 1911, La Hire presented a sequel to this story in Le Mystère des XV ("The Mystery of the Fifteen," later re-published in English as The Nyctalope on Mars). This story introduced the character as Leo Saint-Clair, a famous hero with enhanced abilities called the "Nyctalope" who investigates and fights large-scale threats such as dictators, mad scientists, terrorist organizations, and aliens (multiple books of the series directly reference or use characters from the works of H.G. Wells). Like many American pulp heroes, the Nyctalope often is assisted by friends and allies, including a group he forms called the Committee of Information and Defense Against Evil.

In his early stories, it is said that the Nyctalope's father is Jean (the character seen in the first story from 1908), who was a member of the French Navy. Dismissing his own canon later, author La Hire used the Nyctalope's origin story (published in 1933) to establish that his father is an engineer and chemist named Pierre Saint-Clair. The Nyctalope stories contain other contradictions and gaps regarding the character's past, physical traits, and personal life.

Starting in the 2006, publisher Black Coat Press began releasing new stories featuring the Nyctalope. The same publisher has also released new English language editions of La Hire's original Nyctalope stories.

Publishing history Jean de La Hire (the pen name of Adolphe d'Espi) began his science fiction adventure series in 1908 with the novel L'Homme Qui Peut Vivre dans l'Eau (in English, "The Man Who Could Live Underwater"). In this story, there is a supporting character named Jean de Sainte Clair who is the assistant to Charles Severac, the inventor and captain of a great submarine known as the Torpedo. The story features Severac and Jean de Sainte Clair encountering the mad scientist Oxus. With help from his associates (a monk named Fulbert and surgeon named Balsan), Oxus has created a hybrid shark-man called the Ichtaner, meant to be the first of an army of aquatic super-soldiers who will be unleashed on humanity. Severac is able to defeat Oxus and undo his plans thanks to help from Sainte Clair.

In 1911, La Hire published a sequel to L'Homme Qui Peut Vivre dans l'Eau by featuring the same villain, now years older, in the story Le Mystère des XV (in English, "The Mystery Of The XV"). In this book, La Hire introduces Leo Saint-Clair, a wealthy adventurer with enhanced vitality and night-vision known to colleagues by the nickname of the "Nyctalope." Leo becomes the star of subsequent stories, some of which refer to his father as a naval officer named Jean (implying he is the same character Jean featured in L'Homme Qui Peut Vivre dans l'Eau despite the surname being spelled slightly differently). In 1933 however, the origin story L'Assassinat du Nyctalope ("The Assassination of the Nyctalope") establishes that the Nyctalope's father is named Pierre and that he is a research scientist specializing in electrical engineering and chemistry. The Nyctalope stories contain other contradictions and gaps regarding the character's past, physical traits, and personal life.

In Le Mystère des XV, the villain Oxus from the first book is now the leader of a secret group called the "Society of the XV" who use "radioplanes" (aircraft able to travel on radio waves) to travel to the planet Mars and set up a secret base there. The XV then kidnap 15 women from Earth to take back to Mars as their wives. Koynos, a rival of the Nyctalope, kidnaps Léo Saint-Clair's fiancée Xaviere de Ciserat. The Nyctalope then journeys to Mars to free the kidnapped women. During the adventure, the Nyctalope and the XV encounter native Martians. The book also clearly references the events of the 1898 novel The War of the Worlds as having actually occurred in the world of the Nyctalope, making Le Mystère des XV a fan-fiction sequel of sorts to the famous work by H.G. Wells.

In Le Roi de la Nuit ("The King Of The Night") (1923), La Hire once again borrowed characters from H.G. Wells. The story features Nyctalope using technology developed by Professor Cavor, a fictional scientist who first appears in the 1870 Wells novel From the Earth to the Moon. The same book introduces a new love interest for Saint-Clair, Veronique d'Olbans who is then said to become his wife. No full explanation is offered as to what happened to previous love interest Xaviere. Similarly, Veronique is not seen again after this story.

In La Captive du Démon ("The Demon's Captive") (1927), a religious character named Mathias Lumen states his belief that Saint-Clair is an actual agent of God. He states: "God sometimes allows His infallible justice and rightful wrath to manifest themselves upon the face of this Earth … And YOU are that manifestation! … You, the Nyctalope!" The same story introduces new love interest Sylvie MacDhul, whom the Nyctalope is said to marry. Unlike previous love interests, Sylvie makes more appearances in the subsequent novels. The book Titania (1929) introduces Pierre, the son of Sylvie and the Nyctalope. Sylvie and young Pierre appear again in the 1933 story Les Mystères de Lyon ("The Mysteries of Lyon"). In the 1934 story Le Sphinx du Maroc ("The Moroccan Sphinx"), it is stated that Sylvie died "three years ago" and the Nyctalope is now a widower. His son Pierre is not seen again in later stories.

In 1933, twenty-two years after reintroducing his character as the Nyctalope, La Hire reveals the origin for his character's enhanced abilities in the story L'Assassinat du Nyctalope ("The Assassination of the Nyctalope", later published in English as Enter the Nyctalope). The story reveals that at the age of 20, Léo Saint-Clar encounters villainous nihilists who belong to a group called the Red Circle. During this initial adventure, a gunshot wound miraculously causes Leo to gain perfect night-vision (the side effect being that his eyes sometimes shine with a yellow tint). Later in the story, he is stabbed in the chest but then aided by renowned surgeon and scientist Dr. de Villiers-Pagan who replaces his heart with a mechanical prototype.

In 1940, La Hire also published an anti-French and pro-Nazi volume, Le Crime des évacuations; Les Horreurs que nous avons vues, in which he praised the Nazis for their helpfulness to the French war refugees. During the German occupation of France, he joined the National Popular Rally (RNP) and the Groupe Collaboration. After World War II ended, La Hire was convicted in 1948 of indignité nationale as a collaborator with the Vichy government and Nazi Germany. His books lost popularity, although two more volumes he had partially written were then completed and published by his son-in-law. These two final books were La Sorcière Nue ("The Nude Sorceress") in 1954 and L'Énigme du Squelette ("The Enigma of the Skeleton") in 1955.

La Hire died in 1956 and his books fell into obscurity. During the 20th century, they were not republished and were never translated into other languages. In the 21st century, some volumes of the Nyctalope series were published in English by Black Coat Press, translated either by Brian Stableford or by Black Coat Press editors/publishers Jean-Marc and Randy Lofficier.

Only some the books in the Nyctalope series have been published in English by Black Coat Press. Some of these stories were translated by Brian Stableford while others were translated by Jean-Marc Lofficier and Randy Lofficier.

Following L'Homme Qui Peut Vivre dans l'Eau ("The Man Who Could Live Underwater") in 1909, La Hire's official Nyctalope stories include:

Le Mystère des XV ("The Mystery Of The XV") (1911) - The Nyctalope on Mars, as translated by Brian Stableford and published by Black Coat Press () Lucifer (1921) - Nyctalope vs Lucifer, as translated by Brian Stableford and published by Black Coat Press () L'Amazone du Mont Everest ("The Amazon Of Mount Everest") (1925) La Captive du Démon ("The Demon's Captive") (1927) - translated into English by Michael Shreve and included in The Nyctalope vs. the Antichrist, published by Black Coat Press () Titania (1929) - translated into English by Michael Shreve as The Nyctalope vs. Titania, published by Black Coat Press () Belzébuth (1930) Gorillard (1932) Les Mystères de Lyon ("The Mysteries of Lyon") (1933) - translated into English by Michael Shreve as The Nyctalope - The Witch-Queen of Lyon, published by Black Coat Press () L'Assassinat du Nyctalope ("The Assassination of the Nyctalope") (1933) - Enter the Nyctalope, as translated by Brian Stableford and published by Black Coat Press () Le Sphinx du Maroc ("The Moroccan Sphinx") (1934) La Croisière du Nyctalope ("The Nyctalope's Cruise") (1936) Le Maître de la Vie ("The Master of Life") (1938) - translated into English by Michael Shreve as The Nyctalope and the Master of Life, published by Black Coat Press () Le Mystère de la Croix du Sang ("The Mystery of the Cross Of Blood") (1941) - (adapted into English by Jessica Sequeira as The Cross of Blood and included in The Nyctalope and The Tower of Babel, published by Black Coat Press () Les Drames de Paris ("The Dramas of Paris") (1941) Rien qu'une Nuit ("Only One Night") (1941) - Night of the Nyctalope, as translated by Jean-Marc Lofficier and Randy Lofficier and published by Black Coat Press () L'Enfant Perdu ("The Lost Child") (1942) - The Nyctalope Steps In, as translated by Jean-Marc Lofficier and Randy Lofficier and published by Black Coat Press () Le Roi de la Nuit ("The King Of The Night") (1943) - The Return of the Nyctalope, as translated by Brian Stableford and published by Black Coat Press () La Sorcière Nue ("The Nude Sorceress") (written c. 1940; published 1954) L'Énigme du Squelette ("The Enigma of the Skeleton") (written c. 1940; published 1955)

Fictional biography