Clarence E. Mulford created a character he named Bill (Hopalong) Cassidy and the first novel was released in 1906. I’ve read that Mulford’s idea was that his character had been injured in one of the many disasters that can change the life of a horse-bound farm laborer working around and on top of wild animals. The result of this accident was a broken leg set out on the land the other non-medical personnel present and resulting in a distinctive gate resulting in the nickname.
The character was very popular and 29 novels featuring Hopalong appeared between 1906 and 1941.
In 1935 a movie entitled “Hop-along Cassidy” and staring William Boyd in the title role was released. It was eventually re-released and re-titled as “Hopalong Cassidy Enters”. Thus the hyphenated nickname disappeared and the broken leg was now the result of damage from a gun-shot.
Over the years Hopalong’s outfits became fancier and cleaner. In the first movies he wore many of the trappings that a working cowhand would use but as time passed there was less worn leather and more silver showing. By the early ‘40s Boyd had developed the Hopalong Cassidy “brand” that was black, white and silver mounted.
It may be that Mulford was unhappy with what had been made of his original creation or it could be that he was too busy with other projects but whatever the case when more stories were needed he wouldn’t write them and others had to found. One of those who wrote four Hopalong novels under the pseudo name Tex Burns was Louis L’Amour.
They can be found at the Louis L’Amour trading post http://www.louislamour.com/novels/hopalong4byLouis.htm