Esther is a Biblical heroine. She was an orphaned Jew and one of those who stayed in Babylon while most returned to Jerusalem. Born as "Hadassah", she had been orphaned in infancy and raised by her cousin or uncle (depending on the version of the Bible) Mordecai.
As a young woman, she was sent to King Ahasserus' or Xerxes' (again, depending on the Bible's version) palace and beat other women by the king choosing her to replace Queen Vashti (who had been banished for refusing to attend a feast of his) because of how beautiful she was.
When the king's prime minister, Haman, had said that the Jews should be put to death for disobeying the laws (because unlike the other people, Mordecai wouldn't bow to him, as he [Haman] was an Amalekite, and Amalekites were adversaries of God), there was a decree that disobedient Jews would die.
Esther and her people fasted for three days and was going to the king despite not being summoned. However, instead of being put to death, in fact, instead of being punished, she was spared and allowed to have anything. So, she requested a feast and for Haman to come too. Then, at the feast, she revealed that she was a Jew, much to the King's anger, not with Esther but with Haman, the latter of whom he had hung on the gallows he prepared for Mordecai.
Esther had saved her own people from death.