Esther is a Jewish woman who becomes the queen of Persia and prevents a genocide of her people. The book forms the core of the Jewish festival Purim.
Esther was a member of the Israelites who had been exiled from Jerusalem after its destruction by king Nebuchadnezzar. Esther became an ophan after the death of her parents and is fostered by her cousin, Mordecai. Esther is described as "fair and beautiful", and is chosen as as a concubine for the king and eventually becomes the queen of Persia to replace the former queen who fell from the favor of the king.
Mordecai also becomes a member of the king's palace after he reveals an assasination plot against the king. However, Mordecai is disliked by the king's viceroy Haman who plots to kill Mordecai and builds a gallows to do so. When the king is reviewing court records and realizes that Mordecai had once saved his life but never recieved formal recognition for it, he asks Haman how such a heroic person should be treated. Haman, thinking the king is referring to himself, says the king should dress him in king's clothing and be paraded around on horseback proclaiming his good deeds. And so the king orders Haman to do so on behalf of Mordecai.
Later, the king and queen Esther host a feast to which Haman is invited. At the feast, Esther suddenly reveals that Haman is plotting to kill all the Jews including herself. The king orders Haman hanged on the very gallows Haman had planned to have Mordecai hanged on. In addition, rather than just canceling the decree that Haman and his men be allowed to destroy the Jews, the king reverses it, allowing the Jews to attack their enemies. The Jews are victorious, killing Haman's sons and other opponents of the Jews. Esther sends a letter instituting an annual commemoration of the Jewish people's redemption in a holiday called Purim celebrated ever since. King Ahasuerus remains powerful thereafter and continues his reign with Mordecai as