Hystaspes (hĬstăs´pēz) or Hystaspis (hĬstăs´pĬs), Old Persian Vishtaspa, fl. 6th cent. BC, ruler of ancient Persia, father of Darius I. Under him Darius was governor of Parthia. The legendary patron of Zoroaster is also called Hystaspes or Vishtaspa; he may or may not be the same as Darius' father.