Afternoon reruns of theatrical "B" westerns were the first television appearances of the genre until NBC’s Hopalong Cassidy, adapted from countless Hollywood productions and a radio program, became a children’s favorite in 1949. The first westerns made expressly for television were singing cowboy shows that recycled "B" western stars (e.g. The Gene Autry Show), and formulaic juvenile westerns carried over from successful radio programs (e.g. The Lone Ranger), a trend that continued into the 1950s.

Then in 1955, CBS released the first adult western series, Gunsmoke, adapted from its own groundbreaking radio show whose moral ambiguity and psychologically complex characters broke with the juvenile tradition to address a more mature audience. James Arness was cast in what was to become an iconic leading role as the morose U.S. Marshal Matt Dillon. John Wayne himself introduced the first episode, which proved to be a good marketing strategy, as Gunsmoke stayed in production until 1975, becoming not only the most enduring western series on television, but also the longest running primetime drama.

The success of Gunsmoke prompted the introduction of adult western series on all three networks, resulting in such programs as Cheyenne, Have Gun Will Travel, Maverick, and Rawhide. Television western production peaked in the 1959-60 season with thirty primetime series, but only a handful remained by the 1970s, with Gunsmoke finally going off the air in 1975. Gunsmoke left an enduring legacy, however, with a defining impact on television westerns and a record of twenty years on the air that is still unbroken.