The Shadow is the name of a collection of serialized dramas, originally in 1930s pulp novels, and then in a wide variety of media, and it is also used to refer to the character featured in The Shadow media. One of the most famous adventure heroes of the 20th century United States, the Shadow has been featured on the radio, in a long-running pulp magazine series, in American comic books, comic strips, television, serials, video games, and at least five films. The radio drama included episodes voiced by Orson Welles.

On September 26, 1937, The Shadow radio drama, a new radio series 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 power to cloud men's minds so they cannot see him." As in the magazine stories, The Shadow was not given the literal ability to become invisible.

The introduction from The Shadow radio program "Who knows what evil lurks in the hearts of men? The Shadow knows!", spoken by actor Frank Readick Jr, 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). At the end of each episode The Shadow reminded listeners that, "The weed of crime bears bitter fruit! Crime does not pay...The Shadow knows!" (Some early episodes, however, used the alternate statement, "As you sow evil, so shall you reap evil! Crime does not pay...The Shadow knows!")