"Esther interceding with Ahasuerus"
by cm
Queen Esther by Edwin Long 1878. National Gallery of Victoria, Melbourne
Public DomainQueen Esther by Edwin Long 1878. National Gallery of Victoria, Melbourne - Credit: Wikimedia Commons

Queen Esther, according to the Old Testament Book of Esther, was the Jewish queen of the Persian king Ahasuerus

Raised by her uncle Mordecai, the orphaned Esther married King Ahasuerus after being picked out from the harem.  When Haman, one of the most powerful princes of the realm, plotted to execute Mordecai and kill all Jews in the kingdom, Esther intervened with Ahasuerus to save them. 

The celebration of Purim in Judaism is based on Esther and her story, in commemoration of the deliverance of the Jews.