E.T. Jaynes in PT:TLoS used “Achilles is a real historical person (i.e., not a myth invented by later writers)” in an example. (I don't like it because it's not binary: there's a whole continuum between writers inventing him completely from scratch not based on any real individual at all, and writers having always been as truthful about him as they could have been. I don't think either extreme is true.)