expositor

/ɪkˈspɑzɪtər/
noun
  1. A person who explains or interprets something, such as a text, theory, or idea.
    • She is a well-known expositor of classical philosophy.
    • The museum guide acted as an expositor, explaining the meaning behind each painting.
    • The author served as his own expositor, clarifying the themes of his novel in interviews.