Ahasuerus/Xerxes was the father of Darius the Mede, mentioned in Daniel 9:1 and the king of Persia, mentioned in the book of Esther. There is no doubt that he is the well-known historical Xerxes who reigned from 486-465 B.C.
Identification of this mighty king is found in the King James Version under the name of “Ahasuerus” and the in the New International Version under the name “Xerxes.”
There are also historical correlations. The feast that was held in the 3rd year of the reign of Xerxes at Susa (Est 1:3) corresponds to an assembly held by Xerxes of Greece. The Greek historian, Herodotus (484-425 B.C.), states that Xerxes, following his defeat at Salamis and Plataea, consoled himself in his 7th year with the pleasures of the harem.
This parallels the biblical account that relates that Ahasuerus replaced Vashti by marrying Esther in his 7th year (Est 2:16) after gathering all the fair young virgins to Susa. The Xerxes of Ezra 4:6, whom were written accusations against the Jews of Jerusalem is in all probability the same Xerxes, though sometimes identified with Cambyses, son of Cyrus.
The story of Xerxes is found in the book of Esther.