Otto Wilhelm Rahn was a German medievalist and a Obersturmführer (First Lieutenant) of the SS.
From an early age, he became interested in the legends of Parsifal, Holy Grail, Lohengrin, and the Nibelungenlied. While attending the University of Giessen he was inspired by his professor, the Baron von Gall, to study the Albigensian (Catharism) movement, and the massacre that occurred at Montségur.
In 1931 he traveled to the Pyrenees region of southern France where he conducted most of his research. Aided by the French mystic and historian Antonin Gadal, Rahn argued that there was a direct link between Wolfram Von Eschenbach's Parzival and the Cathar Grail mystery. He believed that the Cathars held the answer to this sacred mystery and that the keys to their secrets lay somewhere beneath the mountain pog where the fortress of Montségur remains, the last Cathar fortress to fall during the Albigensian Crusade.
Rahn believed it was possible to trace the Cathars, who guarded the Holy Grail in their castle at Montsegur, back to Druids who converted to Gnostic Manichaeism. The Druids in Britain were forerunners of the Celtic Christian Church. He saw that the culture of the medieval Cathar stronghold of Languedoc bore a strong resemblance to the ancient Druids. Their priests were akin to the Cathar Parfaits. The Cathar secret wisdom being preserved by the later Troubadours, the travelling poets and singers of the medieval courts of France-M. Sabeheddin.
Rahn wrote two books linking Montségur and Cathars with the Holy Grail: Kreuzzug gegen den Gral (Crusade Against the Grail) in 1933 and Luzifers Hofgesind (Lucifer's Court) in 1937. After the publication of his first book, Rahn's work came to the attention of Heinrich Himmler, the head of the SS, who was fascinated by the occult and had already initiated research in the south of France.
Rahn joined his staff as a junior non-commissioned officer and became a full member of the SS in 1936. Journeys for his second book led Rahn to places in Germany, France, Italy, and Iceland.
Openly homosexual, he was assigned guard duty at the Dachau concentration camp in 1937 as punishment for a drunken homosexual scrape. He resigned from the SS in 1939.
On March 13, 1939 nearly on the anniversary of the fall of Montségur, Rahn was found frozen to death on a mountainside near Söll (Kufstein, Tyrol) in Austria. His death was officially ruled a suicide.