Hopalong Cassidy is a fictional cowboy hero created in 1904 by the author Clarence E. Mulford, who wrote a series of popular short stories and many novels based on the character.
As portrayed on the screen, the white-haired Bill "Hopalong" Cassidy was usually clad strikingly in black (including his hat, an exception to the longstanding western film stereotype that only villains wore black hats). "Hoppy" and his white horse, Topper, usually traveled through the west with two companions-one young and trouble prone with a weakness for damsels in distress, the other comically awkward and outspoken.
When it looked like the character was being retired, William Boyd who played Hopalong Cassidy in 66 pictures gambled his entire future by mortgaging virtually everything he owned to buy the rights and the backlog of movies.
When Hopalong Cassidy was first shown on television it was a huge success making Boyd a star. The Mutual Broadcasting System began broadcasting a radio version of Hopalong Cassidy, with Andy Clyde (later George MacMichael on Walter Brennan's ABC sitcom The Real McCoys) as the sidekick, in January 1950; at the end of September, the show moved to CBS Radio, where it ran until 1952. (Source: wikipedia.org)