Lord Avon is a playwright in Final Fantasy IX who wrote I Want to Be Your Canary, Wishing Upon A Star, and other unnamed works. Not much else is known about him, though his name is a reference to the playwright William Shakespeare, who is popularly known as the "Bard of Avon".
There are inferences that Lord Avon could actually be a member of the same summoner tribe as Dagger and Eiko. According to conversations with the moogles at the Eidolon Wall, the summoner tribe moved to Madain Sari 500 years ago, before which, it can be suggested they settled on the Mist Continent. A failed summoning of Alexander caused the summoner tribe to break Alexander's summoning gem into four pieces and move away in isolation to Madain Sari.
A first edition of Wishing Upon A Star can be found in Madain Sari, and as stated by Garnet Til Alexandros XVII, the book is more than 500 years old, the only other one of its kind being in Alexandria Castle's library. Alexander is known as the holy protector of Alexandria Castle, and the castle also has an extraction circle for extracting eidolons from summoners.