According to the Bible, Hagar was the Egyptian slave of Sarai, Abram's wife (whose names later became Sarah and Abraham). Sarai had been barren for a long time and sought a way to fulfill God's promise that Abram would be father of many nations, especially since they had grown old, so she offered Hagar to Abram to be his concubine.
Hagar became pregnant, and tension arose between the two women. Genesis states that Sarai despised Hagar after she had conceived and "looked with contempt" on her.
–Wikipedia