Hystaspes (Greek form of Old Persian Vishtaspa) can refer to two individuals:

1. A semi-legendary kavi (modern Fårsi key) or "ancient poet and leader" praised by Zoroaster as his protector and a true believer, the son of Aurvataspa (Fårsi Lohrasp). The later tradition and the Shahnama of Firdousi makes him (in the modern form of his name, Key Gushtasp) a "king of Iran". Since Zoroaster probably preached his religion in what is now eastern Iran, Vishtaspa must have been a dynast in Bactria or Sogdiana. The Zoroastrian religion was already dominant in Media in the time of the Assyrian king Sargon (c. 715 BC), and had been propagated there probably in much earlier times; the time of Zoroaster and Vishtaspa was traditionally put at c. 1000 BC.
2. A Persian, father of Darius I, under whose reign he was governor of Parthia, as Darius himself mentions in the Behistun inscription (2. 65). By Ammianus Marcellinus, xxiii. 6. 32, and by many modern authors he has been identified with the actual historical protector of Zoroaster, which runs counter to the received Zoroastrian traditions.