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. This, and the side-effect that his eyes now sometimes have a yellow, reflective coloring, inspires his nickname "Nyctalope". 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.

Jean de La Hire was a prolific French author of numerous popular adventure, science fiction and romance novels.