What nationality was king Ahasuerus?

King Ahasuerus was the king of 127 provinces stretching from India to Ethiopia (Esther ch.1). In the Hebrew Bible his name is vocalized as Achashverosh. He is the "Chshiarsh" of the inscriptions, which was pronounced "Charchash" (Xerxes) in Greek.

He ruled from his throne at the fortress of Susa (Ancient Iran; aka Persia). He was a fickle king, at first agreeing to Haman's request to kill all the Jews but later having Haman hung.