For 18 years, from 1931 to 1949, The Shadow, an unrelenting defender of justice, appeared as the title character in 325 novel-length adventures in The Shadow magazine, making it the first and most important of the character or hero pulps. A prototypical figure named The Shadow had appeared on radio even earlier, on the Detective Story Hour, but the fully-evolved character is best remembered for the radio series that ran from 1937 to 1954, with episodes punctuated by such memorable phrases as "Who knows what evil lurks in the hearts of men? The Shadow knows!" and "The weed of crime bears bitter fruit. Crime does not pay. The Shadow knows!"

The creation of the character named The Shadow is appropriately shrouded in mystery. Although no actual link has been established between the two characters, a seeming prototype of The Shadow appeared in the February 1929 issue of Street and Smith's Fame and Fortune...