Complex sentence: Isaac of Armenia, or "Sahak", Catholicos (or Patriarch) of Armenia (338-439), otherwise known as "Isaac the Great" and sometimes as "Parthev" owing to his Parthian origin.
Split into simpler sentences: Isaac of Armenia, or "Sahak" (338-439) was Catholicos (or Patriarch) of Armenia. He is sometimes known as "Isaac the Great," and as "Parthev" owing to his Parthian origin.