Hagar is a biblical woman. According to the Book of Genesis, she was an Egyptian slave, a handmaiden of Sarah (then known as Sarai), whom Sarah gave to her own husband Abram (later renamed Abraham) as a wife to bear him a child. Abraham's firstborn son, through Hagar, Ishmael, became the progenitor of the Ishmaelites, generally taken to be the Arabs.
In Genesis 21, the story of how Sarah forced Abraham to send Hagar away went as follows: Early the next morning, Abraham brought Hagar and Ishmael out together. Abraham gave Hagar bread and water and sent them into Beersheba's wilderness. She and her son wandered aimlessly until their water was consumed entirely. In a moment of despair, she burst into tears. God heard her and her son crying and came to rescue them. The angel opened Hagar's eyes and she saw a well of water. He also told Hagar that God would "make a great nation" of Ishmael. Hagar found her son a wife from Egypt and they settled in the Desert of Paran.