Originally appearing in the pages of Black Mask, under the watchful eyes of then-editor Joseph Shaw, Flashgun Casey was the originally fast-talking crime photographer, a big, hot-tempered Boston Mick with a gift for gab and a nose for trouble. No "artiste", Casey kept a bottle of hooch and a .38 in his desk drawer, and boasted of being able to put a "slug where he aimed" and having "two big fists he knew how to use". He appeared in several short stories in the pulps and several novels.
Casey, whose first name was never revealed, was the major crime photographer at the fictional Morning Express newspaper. With the help of reporter Ann Williams, he tracked down criminals and solved numerous crimes on this popular mystery-adventure series. Often a picture snapped at a crime scene led Casey to play detective.