What was Hopalong Cassidy's horse's name ?
Its name is Topper. Hopalong Cassidy or Hop-along 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.
In his early writings, Mulford portrayed the character as rude, dangerous, and rough-talking. From 1935, the character—as played by movie actor William Boyd in films adapted from Mulford's books—was transformed into a clean-cut hero. Sixty-six popular films appeared, only a few of which relied on Mulford's stories. Mulford later revised and republished his works to be more consistent with the character's screen persona. "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 older, comically awkward and outspoken.