October 12, 1937: Mr Keen , the longest running detective show, aired for the first time on radio . The show starred Bennet Kilpack as Mr. Keen, Arthur Hughes, and Phil Clark. The program was sponsored by BiSoDol antacid mints, Hill's cold tablets, Heet liniment, Dentyne, Aerowax, RCA Victor and Chesterfield cigarettes. Some sponsors lasted for the entirety of the show's history, but many changed throughout the running of the program. Mr. Keen , otherwise known by its full title Mr. Keen, Tracer of Lost of Persons , was first broadcast on NBC Blue Network before it moved to CBS in 1947, 10 years after its debut. During the first few episodes of the show, the "Tracer of Lost Persons" part was kind of forgotten, as most of Mr. Keen's cases involved murder. The show lasted for nearly 20 years, with the last episode airing on April 19, 1955.