Aaron Marc Stein, known by the pen name George Bagby, was an American novelist who specialized in mystery fiction. Bagby's focus was on police investigators, especially the fictional Inspector Schmidt, Chief of Homicide for the New York Police Department. In the Schmidt novels, mystery-writer Bagby himself appears as "the Watson to Schmidt's Holmes, following him on cases, and acting as biographer." A number of his novels have been translated into other languages, including German, French, and Spanish.