One of the most famous adventure heroes of the 20th century United States, the Shadow has been featured on the radio

The Shadow, created by writer Walter Gibson (a.k.a. Maxwell Grant) for Street and Smith's pulp The Shadow Magazine in 1933. Street & Smith (Publishers) entered into a new broadcasting agreement with Blue Coal in 1937, and that summer Gibson teamed with scriptwriter Edward Hale Bierstadt to develop the new series. The Shadow returned to network airwaves on September 26, 1937, over the new Mutual Broadcasting System. Thus began the "official" radio drama, with 22-year-old Orson Welles starring as Lamont Cranston, a "wealthy young man about town." Once The Shadow joined Mutual as a half-hour series on Sunday evenings, the program did not leave the air until December 26, 1954. Welles did not speak the signature line, "Who knows what evil lurks in the hearts of men?" Instead, Readick did, using a water glass next to his mouth for the echo effect. The famous catch phrase was accompanied by the strains of an excerpt from Opus 31 of the Camille Saint-Saëns classical composition, Le Rouet d'Omphale. More here from Wikipedia