Name Kyus

or Kawus (early Islamic sources: کیوس) was the eldest son of Kavadh I, the Sasanian emperor of Iran.

Kawus might have initially been the heir presumptive to the Sasanian throne. However, following the outbreak of the Mazdakite revolt, Kawus was accused of supporting Mazdak and adhering to his heresy. His younger brother, Khosrau I Anusheruwan who was known for his support of orthodox Zoroastrianism, was favoured by the nobles and the Zoroastrian clerics. As a result, Kawus was passed over as the heir and the throne was offered to Khosrau.
A few sources suggest that Kawus was given the governorship of the northern province of Padishkhwargar and lived there honorably. He is also allegedly the ancestor of the Bavand Dynasty of Tabaristan who ruled that region for many centuries after the advent of Islam.
Kawus was probably named after the mythical/legendary king Kay Kawus (Avestan Kauui Usan). The names of his father and his brothers also suggest a renewed late Sasanian interest in the Iranian legendary history and particularly the Kayanid Dynasty.