Esther is the eponymous heroine of the Book of Esther. Set in the Persian Achaemenid Empire, it tells how king Ahasuerus seeks a new wife after his queen, Vashti, is deposed for disobeying him. Esther (called Hadassah when first introduced) is chosen to fulfill this role due to her beauty. Ahasuerus' grand vizier, Haman, is offended by Esther's cousin and guardian, Mordecai, due to his refusal to prostrate himself before Haman. Consequently, Haman plots to have all the Jewish subjects of Persia killed, and convinces Ahasuerus to permit him to do so. However, Esther foils the plan by revealing Haman's eradication plans to Ahasuerus, who then has Haman executed and grants permission to the Jews to kill their enemies instead, as royal edicts (including the order for eradication issued by Haman) cannot be revoked under Persian law.

Her story provides the traditional explanation for the Jewish holiday of Purim, celebrated on the date given in the story for when Haman's order was to go into effect, which is the day that the Jews killed their enemies after the plan was reversed. The book exists in two distinct forms: a shorter Hebrew version found in Jewish and Protestant Bibles, and a longer Greek version found in Catholic and Orthodox Bibles.