Elizabeth Weingarten in Slate:
According to the Bible, Hagar was an Egyptian slave sent to the bed of her master, Abraham, by his barren wife, Sarah. When Hagar became pregnant with Ishmael—who would become Abraham's heir—the formerly submissive servant turned haughty and began to treat Abraham's lawful wife with “contempt.” Sarah punished Hagar for her attitude and sent the slave packing. (An angel of God eventually persuaded a chastened Hagar to return to the couple.) Several years later, after God restored Sarah's fertility and she gave birth to Isaac, Sarah began, once again, to fiercely resent her husband's concubine. “Cast out this slave woman with her son!” she demanded of Abraham. In an instant, Hagar was banished a second time. Her lesson: Any power she had ever acquired was ephemeral, contingent on factors beyond her ability to please her lover or bear him a healthy son. The mistress's pride was no match for the wife's wrath.
Several millenniums later, the mistress remains a tenuous position, as historian Elizabeth Abbott explores in her new book, Mistresses: A History of the Other Woman, out this week. Since Hagar's era, however, a handful of women have learned to parlay their scandalous relationships into positions of power—and some have changed history in doing so.