The Shadow is the name of a collection of serialized dramas, originally in 1930s pulp novels, and then in a wide variety of media. Its title character 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 feature films. The radio drama included episodes voiced by Orson Welles.

Originally created to be a mysterious radio-show narrator, The Shadow was developed into a distinctive literary character in 1931 by writer Walter B. Gibson.

The Shadow debuted on July 31, 1930, as the mysterious narrator of the radio program Detective Story Hour, which was developed to boost sales of Street & Smith's monthly pulp Detective Story Magazine. When listeners of the program began asking at newsstands for copies of "that Shadow detective magazine," Street & Smith decided to create a magazine based on a character called The Shadow and hired Gibson to create a character concept to fit the name and voice and write a story featuring him. The first issue of The Shadow Magazine went on sale on April 1, 1931, a pulp series.

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." 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, 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!").