Three years before beginning a landmark run on television, Gunsmoke burst onto radio airwaves.
Originally envisioned as a Western in the mold of Philip Marlowe, Gunsmoke starred William Conrad as Marshal Matt Dillon, "the first man they want to see, and the last one they want to meet", as Conrad intoned at the beginning of each episode. Conrad narrated most, if not all, episodes from Dillon's point of view. The supporting cast included Georgia Ellis as Miss Kitty, Howard McNear (later of The Andy Griffith Show), easily recognizable vocally as Doc Adams, and Parley Baer as Chester, Dillon's deputy. Baer would also find his way to Mayberry, cast as the Mayor in a few episodes of The Andy Griffith Show, but what some of you might not know is that Baer was also the voice of Ernie Keebler in all those animated cookie commercials.
There was a time when the TV & radio shows were actually running concurrently, though not on the same night. It's said that Conrad, because of his size, was never considered to transition to the TV version, hence James Arness being cast as Dillon for TV, and becoming an icon in the process.
The Internet Archive serves up a 1957 episode, "The Peace Officer". Announcer Jack Walsh worked on both the radio & TV versions all the way to the latter's end in 1975.