This should be explained to our members who are not Americans.
Karl Marx (1818-1883) was a 19th-century German philosopher who is generally regarded as the founder of communism. In fact, communism is still sometimes called "Marxism."
Harpo Marx (real name "Arthur") 1888-1964, on the other hand, was an American comedian. His brothers and he, known professionally as the Marx Brothers, were a comedy team who made many comedy movies--mostly of the slapstick kind (physical humor rather than words) and were extremely popular.
Arthur was a musician who played the harp, and before long he adopted the name "Harpo." In the group's movies and TV shows, there was always an interlude during which he played his harp--very well.
Harpo was probably the least crazy of the family--and surely the sweetest. When someone asked him why he and his wife had built an enormous house, he said, "I’d like to adopt as many children as I have windows in my house. So when I leave for work, I want a kid in every window, waving goodbye."
Groucho (Julius Henry) Marx (1890-1997) was the most successful and best-known of the family. Long after the family stopped working together in movies (slapstick is very hard work), Groucho had a long career as the M.C. on a quiz show called "You Bet Your Life." It started out on radio, then switched to television when TV was invented.
Not to ignore Karl Marx, he is still well-known as the father of communism.