On September 26, 1937, The Shadow, a new radio drama based on the character as created by Gibson for the pulp magazine, premiered with the story "The Death House Rescue", in which The Shadow was characterized as having "the hypnotic power to cloud men's minds so they cannot see him". In the magazine stories, The Shadow did not become literally invisible.
The introductory line from the radio adaptation of The Shadow – "Who knows what evil lurks in the hearts of men? The Shadow knows!" - spoken by actor Frank Readick, has earned a place in the American idiom. These words were accompanied by an ominous laugh and a musical theme, Camille Saint-Saëns' Le Rouet d'Omphale ("Omphale's Spinning Wheel," composed in 1872).
The Shadow, at the end of each episode, reminded listeners, "The weed of crime bears bitter fruit! Crime does not pay...The Shadow knows!"
