I believe James Arness got the Gunsmoke job on the recommendation of John Wayne, who turned the job down. Good move for both.
http://www.youtube.com/watch?v=T646gNcRiMs
Here is that introduction/
Arness was in the movie Hondo with Wayne.
The radio version of Gunsmoke is good too. William Conrad played Matt. The radio cast thought they were the naturals for the upcoming TV version.