Isaac of Armenia, or Sahak (338 – 439) was Catholicos (or Patriarch) of Armenia. He is sometimes known as "Isaac the Great," and as "Սահակ Պարթև / Sahak Parthev" in Armenian, owing to his Parthian origin. Isaac was son of the Christian Saint Narses and descended from the family of Saint Gregory the Illuminator. He was the fifth catholicos of the Arsacid Dynasty of Armenia after St. Gregory I the Enlightener (301-325), St. Aristaces I (325-333), St. Vrtanes I (333-341) and St. Husik I (341-347).