Who are the main characters in "Jonathan Livingston Seagull" besides the hero Jonathan?

Jonathan is described in the link referenced below as the only true major character in the book.  The other characters are all considered to be minor characters, and more or less thematic stereotypes.  Old Chiang is wise and mystical, Fletcher Lynd Seagull is young and eager, and Martin William Seagull is a cripple who overcomes his handicap through the power of his mind and learns to fly.