Louis Maigret (or Meigret) was the author of the Traité de la Grammaire française, which was published in 1550. This was the first grammatical description of (Middle)French.
References
Book: Malmberg . Bertil . Histoire de la linguistique: de Sumer à Saussure . 1991 . Presses universitaires de France . Paris . 9782130433576 . 1. éd.