After losing both of his arms, skilled machinist Chester Morisi developed a set of prosthetic arms that also housed a set of basic guns. Dubbing himself as Handgun he embarked on a life of crime. He soon built a complex weapons lab, located in a sub-basement of the apartment tenement where he lived. It was accessed via a secret elevator.
Over the years, he expanded his skill in cybernetic mechanics and constructed a broad array of artificial arms, each with their own unique weapons capabilities.
Handgun used many different weapons-enabled artificial arms to commit crimes.
His last name is likely a reference to Charlton Comics cartoonist and creator of Peter Cannon Thunderbolt Pete Morisi.