Who was Sarah's Egyptian handmaid, Hagar?

Hagar with her son, Ishmael.

       HAGAR (Gen. 16:1, 3, 4, 8, 15, 16; 21:9, 14, 17; 25:12), Sarah's Egyptian handmaid, obtained probably while she and Abraham were in Egypt. The maid became the mother, through Abraham, of Ishmael, from which came the tribe of Ishmaelites, who were nomads of northern Arabia.
       When Sarah was 76 years old (according to the way of reckoning time then) and had failed to conceive the heir God had promised, she followed a custom of the times, that of giving her maid Hagar to her husband. And Hagar became the earthly channel for what Sarah thought was the Heir of Promise.
       When Hagar had been raised to the place of secondary wife by her mistress, her pride became inflated and she was insolent to Sarah. Her actions caused Sarah to complain to her husband, who told her to do with her maid as she pleased. Upon being reprimanded by Sarah, Hagar fled to the wilderness.
       The angel of the Lord found Hagar by a fountain of water and inquired of her what had happened. Hagar announced that she was fleeing from her mistress. The angel then announced to Hagar that she would conceive by Abraham and that her seed would be multiplied for posterity. Hagar's child was born and named Ishmael.
       About 14 years later the angel told Abraham that Sarah would bear a son in her old age, and that she would be a mother of nations. This Heir of Promise, Isaac, was born when Hagar's son Ishmael was about 14 years old. Sarah weaned her child when he was about three years of age and celebrated the weaning with a festival. But Hagar and her son Ishmael stood off mocking Sarah's child.
       Sarah said to Abraham, "Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son" (Gen. 21: 10). Abraham yielded after an angel had told him that Isaac was the son through whom God's promises would be fulfilled.
       Early one morning Abraham arose and placed a goatskin of water upon Hagar's shoulder and sent her with Ishmael into the wilderness. After the water was gone, Hagar cast her son under a shrub to die and lifted up her voice and wept.
       When God heard Ishmael crying, he told Hagar to fear not, but to arise, for he would make of Ishmael a great nation. Then she opened her eyes and saw a well of water and gave her son a drink.
       The child grew and dwelt in the wilderness of Paran. The final account in Genesis states that "his mother took him a wife out of the land of Egypt."
       The concluding Biblical record of Hagar is in Galatians 4:24-25, where she is referred to as Agar. Paul speaks of her, a bondwoman, and Sarah, a freewoman, saying: "Which things are an allegory: for
these are the two covenants; the one from the mount Sinai, which gendereth to bondage, which is Agar. For this Agar is mount Sinai in Arabia, and answereth to Jerusalem which now is, and is in bondage with her children." The allegory compares the child of the flesh and the child of the spirit.
       Many traditions have arisen around the name of Hagar. One is that after Sarah's death Abraham took Hagar for a wife. Abraham's second wife was Keturah, meaning "separation."
       Other traditions center around Hagar and Mecca and the holy well of Zem-Zem, in the sacred area surrounding the Kaaba, or holy building. In the cornerstone here is said to be the original Koran of the Mohammedans. At this well Hagar and her son were supposed to have quenched their thirst.
       From the Arabs of the Hagar-Abraham line, Mohammed was descended, say Mohammedans. The strength of Islam, still mighty on three continents, is said to be bound up with the name of Hagar.