1) Animal Crackers brothers 2) Any of five O-ending brothers 3) Big critic of capitalism 4) Big name in economics history 5) Brothers in Animal Crackers 6) Brothers seen in Duck Soup 7) Capital fellow 8) Chico 9) Chico or Harpo 10) Class-action philosopher 11) Collaborator with Engels 12) Comedian 13) Comedic actor Groucho Found on https://www.crosswordclues.com/clue/marx