Musicians/actors/vaudevillians - Groucho, Harpo, and Chic(k)o the nucleus. They left their mother's act and became headliners on their own. Zeppo replaced Gummo (they were "The Four Marx Bros"); they jumped to Broadway (better pay/status) - their first films (Cocoanuts and Animal Crackers) were adaptations of their hits. Zeppo left, as did the "Four". They were fast, either with wordplay, insults, or sight gags - sharper and more highbrow than the Three Stooges (YMMV).