‘A man of letters' means-

The phrase "a man of letters" does not refer to a fool, stupid person, cunning man, or anyone with negative connotations.

It actually means a learned or highly educated individual, especially one with expertise in literature or writing. So, the closest option would be:

c) a wise person

However, "wise person" is a broader term, while "a man of letters" specifically refers to someone with knowledge and accomplishment in written language and literature. Think of it as someone who possesses literary and intellectual wisdom.