The most successful Western in television history got its start on radio, like a number of other television series in the 50's. The only difference is, Gunsmoke far outlasted The Life of Riley, The Jack Benny Program, Gang Busters, Dragnet, and so on, lasting 20 years before CBS ended the series in 1975.
Most folks knew about the town of Dodge City from the stories of Wyatt Earp and Doc Holliday. However, they weren't around when Marshal Matt Dillon (James Arness) was in charge, which suggests that Gunsmoke is set well after the "Gunfight at the OK Corral". On radio, William Conrad, better known for his television work (i.e. Cannon), played Dillon. Arness simply picked up the baton and ran with it, playing Dillon with the same intensity that Conrad had (I have to assume; I've never heard the radio version, but judging from Conrad's TV work, well......).
Dillon had a handful of deputies during the course of the show's run, including Chester Goode (Dennis Weaver) and, of course, Festus Haggen (Ken Curtis, formerly of the Sons of the Pioneers). For most of the series' run, the core cast was filled out with Doc Adams (Milburn Stone) & Miss Kitty, the owner of the Long Branch Saloon (Amanda Blake). In the early years, Gunsmoke was a half-hour show (syndicated under the title, Marshal Dillon) before expanding to the 1 hour format everyone knows. I actually got the chance to see those half-hour reruns when they aired on Retro a few years back, but I don't know of anyone that has them now. The one-hour edition airs on Me-TV and, I think still, TV Land, among other places.
Here's a sample episode from the half-hour era:
In time, the series would expand to an hour, and would remain so for the rest of the run.
The popularity of Gunsmoke was such that they would bring the cast together again for some TV movies in later years.