Excalibur
Geoffrey of Monmouth, in his "Historia Regum Britanniae" ("The History of the Kings of Britain", c. 1136), Latinised the name of Arthur's sword as "Caliburnus" (potentially influenced by the Medieval Latin spelling "calibs" of Classical Latin "chalybs", from Greek "chályps" ["χάλυψ"] "steel"). Most Celticists consider Geoffrey's "Caliburnus" to be derivative of a lost Old Welsh text in which "bwlch" (Old Welsh "bulc[h]") had not yet been lenited to "fwlch" (Middle Welsh "vwlch" or "uwlch"). In the late 15th/early 16th-century Middle Cornish play "Beunans Ke", Arthur's sword is called "Calesvol", which is etymologically an exact Middle Cornish cognate of the Welsh "Caledfwlch". It is unclear if the name was borrowed from the Welsh (if so, it must have been an early loan, for phonological reasons), or represents an early, pan-Brittonic traditional name for Arthur's sword.
Scientology and the occult
Scientology founder L. Ron Hubbard claimed to have had a near-death experience in 1938 that inspired him to write "Excalibur", an unpublished manuscript based on the revelations from the experience. In 1945–46, Hubbard was briefly involved with and defrauded Jack Parsons, an American rocketry pioneer who was also a devoted Thelemite and member of the Agape Lodge of Aleister Crowley's magical order, Ordo Templi Orientis, in Pasadena, California. In 1950, Hubbard published "", and in 1953 he organized the Church of Scientology.