JS Bach (1685-1750)
I have a wild notion that Bach perfected music with the Well tempered Clavier. It is so perfect, in my eyes, that it would take something special to move music in a different direction. One of his final works was the Art of the Fugue, which was left unfinished. Perhaps he had ran out of ideas.
I wonder if he had worked out where music was going, mathematically and had provisionally outlined every major work that would be composed, to the 20th century. So he wrote it all down in a Principia Musica or something and only gave it to initiated musicians, like his sons and Haydn. Ludicrous idea, I know.