Ahasuerus is the name applied in Scripture to three rulers: the father of Darius the Mede, a king mentioned in Ezra, and the Persian king in Esther. The name is associated with Median and Persian kings.
The Ahasuerus of Esther ruled Persia, Media, and Babylonia from India to Ethiopia. Esther was chosen as his queen. Another Ahasuerus is mentioned in the account of opposition to the rebuilding of Jerusalem, and one appears in Daniel as the father of Darius the Mede.
The three rulers are identified respectively with Cyaxares I, Cambyses, and Xerxes in the supplied historical comparisons. The Esther ruler succeeded Darius and reigned twenty-one years; the Greek version of Esther uses the name Artaxerxes.