Ahasuerus (Xerxes) was a king of Persia and the husband of Esther (Ester). Scholars generally agree that Ahasuerus is the same person as Xerxes I (485-464 B.C.). In ancient societies, kings sometimes were known by more than one name, especially if they reigned in a community in which more than one language was widely spoken.
The book of Esther tells the story of how Ahasuerus banished his queen, Vashti, and then later chose Esther to be his queen. Ahasuerus' advisor, Haman, however, hated the Jews, and he prevailed upon Ahasuerus to order them to be wiped out throughout Persia.
During a sleepless night, Ahasuerus sent for his royal records and read of how a Jew named Mordecai, who was Esther's guardian, had uncovered a plot to kill the king and thus saved his life. Ahasuerus' discovery led to Mordecai's being raised to a position of honor within the kingdom.
Haman's treachery soon led to his own fall, and he and his ten sons were hanged on the gallows he had previously prepared for Mordecai.
In Ezra 4:6, the reign of Ahasuerus is mentioned chronologically between Cyrus and Artaxerxes. The name Ahasuerus means "mighty man."