Isaac de Porthau (also Portau or Portaut; January 30, 1617, Pau – July 13, 1712) was a Gascon black musketeer of the Maison du Roi in 17th century France. In addition, he was the first cousin once removed of the Comte de Troisville, captain of the Musketeers of the Guard, and first cousin of Armand d'Athos. Porthau served as the inspiration for Alexandre Dumas's character "Porthos" in the d'Artagnan Romances.