According to the Bible (Esther 2:7), she was orphaned and either adopted or fostered (scholars are unclear about how to interpret the text) by her uncle (or cousin), Mordecai.

She is famous in Jewish history as the queen (she was the wife of King Ahashueros) who saved the Jews from the genocidal plot of Haman, whose downfall in 356 BCE is celebrated during the Purim festival.

References

The Complete Who's Who in the Bible, edited by Paul Gardner. (London: Marshall Pickering, 1995)
Encyclopaedia Judaica, edited by Cecil Roth. (Jerusalem: Keter Publishing House, 1971)
New Standard Jewish Encyclopedia, editor-in-chief Geoffrey Wigoder. 7th edition. (New York: Facts On File, 1992)
Prero, Yehuda. "Purim." Available at: http://www.torah.org/learning/yomtov/purim/
Microsoft Encarta 98 Encyclopedia, 1993-97

Indexes

Mythological, Traditional and Divine Figures
Jewish
Near East
Iran
Israel
Palestine
Bce
Rulers, Nobles, Chiefs, Presidents, Prime Ministers
Figures Whose Adoption or Fostering Is Fictitious, Disputed or Unconfirmed
Orphaned (Both Parents)
Uncles and Aunts, Parents' Uncles and Aunts
Cousins, Parents' Cousins
Wealthy, Famous, Noble or Divine Adoptive or Foster Families
Parent(s) Died, Disappeared or Became Incapacitated