A multimedia cowboy hero, Hopalong Cassidy first appeared in a series of magazine stories that were published in 1905 and 1906. Clarence E. Mulford, who was residing in Brooklyn at the time and had never been West, was the author. His Cassidy was a tough, tobacco-chewing redhead, who bossed the hands at the Bar-20 Ranch and got his nickname from the fact that a gunshot wound in his leg had left him with a permanent limp. The more familiar image of this popular American fictional hero, however, is the one personified in movies and on television by silver-haired actor William Boyd. Boyd's Hopalong Cassidy was a dapper, soft-spoken cowboy, who almost always wore black, and was taken into the hearts of millions of kids. In his later television incarnation, Hopalong products became one of the first merchandising sensations inspired by television.

Mulford, who worked for over 20 years in...