Hassan-i Sabbah
The Nova Trilogy (as well as a passage in the book on the cut-up technique named "Minutes to Go") feature the character Hassan-i Sabbah and his final words "Nothing is true—everything is permitted." Burroughs was introduced to Hassan through Betty Bouthoul, who had written an extensive book on the assassins titled "The Master of the Assassins" (French title "Le grand maître des Assassins").