The Pope has it but he does not use it. Your father has it but your mother uses it. Nuns do not need it. Arnold Schwarzenegger has a big one, Michael J. Fox's is quite small. What is it?

Why this works

This riddle cleverly plays with the concept of "last name," creating humorous associations that lead to the answer. The Pope has a last name (Bergoglio), but he is typically referred to simply as "the Pope," not by his last name. Your father has a last name, which is often used by your mother when she takes his name in marriage. Nuns usually adopt a religious name and forgo their last names, and the references to Arnold Schwarzenegger and Michael J. Fox highlight the varying lengths of their last names—Schwarzenegger being long and Fox being short. Each clue creatively hints at the idea of a surname without directly stating it, making the riddle engaging and thought-provoking!