The Shadow was originally created as a host for a radio show to help promote Detective Story Magazine (published by Street and Smith Publishing). What made the character the Shadow popular with listeners was his sinister laugh. Because of the Shadow's popularity, Street and Smith held a contest asking listeners to describe the Shadow, based on 10 clues given on the radio show.
The result of this contest would turn the Shadow from a faceless voice on the radio into a character who wore a cloak and had excellent athletic abilities, superb marksmanship, and a quick wit. Then in April of 1931, The Shadow magazine came out with a story called "The Living Shadow", written by Walter Gibson. The magazine became so popular, it went from monthly to bi-monthly.
In 1937, the Shadow appeared on film and his radio show was re-done to include the Shadow as both the narrator and the main star. Orson Wells was the radio voice of the Shadow until 1939. In 1938, with Superman's appearance on the scene and more superheroes popping up every minute, the Shadow was given the super-ability to render himself "invisible" by clouding people's minds. In 1940, Shadow Comics #1 appeared and both this and the magazine would last until 1949. The radio show lasted until 1954.
Since then, several revivals of the character have occurred: