Hopalong Cassidy's horse was named Topper. The horse was discovered on a ranch in 1937 and named Topper by the wife of the actor who played Hopalong Cassidy on film and television. The horse was named after the "Topper" book series by Thorne Smith.
There were a total of 66 films depicting the adventures of fictional cowboy Hopalong Cassidy. Topper did not appear in the first film, which came out in 1935, but after Hopalong's actor William Boyd bought him in 1937, he was used in subsequent films, television episodes, and even parades and other public appearances. Boyd rode Topper until his retirement in 1953. Topper died in 1961 and is buried in Los Angeles Pet Memorial Park.