The Avenger is a fictional character whose original adventures appeared between September 1939 and September 1942 in the pulp magazine The Avenger, published by Street and Smith Publications. Five additional short stories were published in Clues Detective magazine (1942–1943), and a sixth novelette in The Shadow magazine in 1943. Newly-written adventures were commissioned and published by Warner Brother's Paperback Library from 1973 to 1974. The Avenger was a pulp hero who combined elements of Doc Savage and The Shadow though he was never as popular as either of these characters. The authorship of the pulp series was credited by Street and Smith to Kenneth Robeson, the same byline that appeared on the Doc Savage stories. The "Kenneth Robeson" name was a house pseudonym used by a number of different Street & Smith writers. Most of the original Avenger stories were written by Paul Ernst.
In 1941 Walter Gibson turned The Avenger into a radio series that lasted 26 episodes. His origin and powers were so radically altered that this Avenger should probably be considered a brand new character. In the radio version The Avenger is biochemist Jim Brandon, who secretly fights crime using his inventions, a "Telepathic Indicator" which allows him to pick up thought flashes, and a "Diffusion Capsule" which provides a black light of invisibility. He is assisted by Fern Collier, the only person he trusts with his secret identity. per The Avenger page at International Catalog of Superheroes.
For a more in depth look at The Avenger, check out the extensive Wikipedia page.