Westerns have been a fixture on American television for nearly as long as the medium has been around. Among the first were "Hopalong Cassidy" and "The Lone Ranger," both of which featured clean-cut cowboy heroes. In the early westerns, the gunslinging good guys wore white hats, while their nefarious nemeses were marked by their black hats. As the genre evolved, so did the cowboys, no longer neatly divided into heroes and villains, and the "white hats" and "black hats" took on shades of gray. Here's a look back at the evolution of the western on the small screen in terms of their ten-gallons.