Wild Bill Hickok
The Wild Bill Hickok radio series was first heard on the Mutual Radio Network in 1951.  The series continued through 1956.  Hickok was a solid cowboy hero of the kids along with his faithful sidekick "Jingles",  played by Andy Devine.  Guy Madison played Marshal Wild Bill Hickok on his horse named "Buckshot" while Jingles rode "Joker". 

Both actors continued the series as it moved to TV in the early 50's following a format developed by the Lone Ranger and other westerns including Gene Autry, Roy Rogers and the Cisco Kid to mention a few.