To read about Queen Esther please check out this wikipedia page.
This is the annual feast of Purim, in memory of their deliverance. Haman set the date of Adar 13 to commence his campaign against the Jews. This determined the date of the festival of Purim.
Who is Haman? A nasty dude if there ever was one.
Haman informed the king that the Jews were a useless and turbulent people and inclined to disloyalty, and he promised to pay 10,000 silver talents into the royal treasury for the permission to pillage and exterminate this alien race. The king then issued a proclamation ordering the confiscation of Jewish property and a general extermination of all the Jews within the empire of the Persian King Ahasuerus.
Esther lived under the protection of her cousin Mordecai, and after a convoluted story ended up in the kings harem to become his future wife.
Esther dressed in her royal apparel and went before the king, who was pleased to see her. When the king asked her what her request was, she invited the king and Haman to come to a banquet she had prepared. At the banquet they accepted her invitation to dine with her again on the following day. Haman, carried away by the joy that this honour gave him, issued orders for the erection of a gallows on which he intended to hang the hated Mordecai
Only at the second dinner party, when the king was sufficiently beguiled by her charms, did Esther reveal for the first time her identity as a Jew, and accused Haman of the plot to destroy her and her people. The king ordered that Haman should be hanged on the gallows prepared for Mordecai, and, confiscating his property, bestowed it upon the intended victim.
Here is a much better, and funnier delivery of the whole story of why we celebrate Purim by the comedian Mayim Bialak.
And this is how to make hamantaschen the best part of the holiday: