Esther (or Ester) was the daughter of Abihail, of the tribe of Benjamin. She was the cousin, and the adopted daughter, of Mordecai. On the orders of the Persian King Ahasuerus, Esther replaced Vashti as queen. And at Mordecai's request, Esther concealed her Jewish birth.
After Haman, the king's chief minister, found out that his foe, Mordecai, was Jewish, he devised a plan to have all Jews killed. Haman secured the king's permission to have a massacre of all Jews in the Empire by the end of that year, on the14th day of the month of Adar. Haman built a gallows to hang Mordecai.
Esther, however, acted to foil the plot. She revealed to the king that she was Jewish, and that the Jews were destined to be massacred by orders from Haman. Haman's last-minute appeal to the queen's mercy was misinterpreted by the king as an attempt at seduction, and the king ordered that Haman be hung on the same gallows he had built for Mordecai. Esther reminded the king that the decree of extermination was still in effect.
Ahasuerus informed her that a royal edict could not be revoked, and instead issued a counter-edict, permitting the Jews to arm and defend themselves. When the day arrived, the Jews were so successful in defending themselves that they observed a new feast. In commemoration of these events, Esther and Mordecai instituted the annual festival of "Purim," which means "throwing dice," taken from the Persian word "Pur." Esther and Mordecai were awarded Haman's estate.
Details about the life and times of Esther are contained in the Bible's book of Esther.