Sarah

(ca. 1802 B.C.E. – ca. 1675 B.C.E.) The first of the Imahot, “Founding Mothers” of the Jewish People; the wife and “teaching partner” of Avraham. Like all the Imahot, she could not bear children initially. This was because Hashem wanted to “hear” their reaction to this frustration. She bore Yitzchak miraculously at the age of ninety, when her youthful characteristics returned to her. When Yishmael, the son of Hagar, her hand-maiden mocked Yitzchak, she ordered Avraham to drive him and his mother away, saying “the son of this hand-maiden will not inherit together with my son, with Yitzchak.” (Bereshit 21:10) And when Avraham objected to this harsh treatment of his son, Hashem confirmed Sarah’s orders when He said, “…Everything that Sarah has told you, do not fail to do…” (Bereshit 21:12) After Sarah dies, the Midrash testifies that Sarah was as free of sin at the age of one hundred as she was at twenty and as beautiful at twenty as she had been at seven.” (Bereshit Rabbah)

Taken from: http://www.ou.org/about/judaism/s.htm#sarah