Hopalong Cassidy is a fictional cowboy character created by author Clarence E. Mulford in the early 1900s. He first appeared in a series of short stories and novels, becoming popular for his adventurous spirit and moral integrity. The character is known for his signature black outfit and his trademark phrase, "Howdy, partner!" In the 1930s, Hopalong Cassidy transitioned to film and television, starring in numerous movies and a successful TV series. Portrayed by actor William Boyd, he became a cultural icon, appealing to audiences with his charm and heroism. The character's popularity helped shape the Western genre in American entertainment.