A character from the Hebrew Bible/ Old Testament - Genesis 16-25 . Hagar is the slave girl of Sarah wife of Abraham. When Sarah could not bear children she sent her slave girl Hagar to Abraham instead, since under ancient custom a wife could give a slave to her husband in place of herself and still consider the slave's children her own. When Hagar became pregnant Sarah grew jealous and mistreated Hagar. Hagar ran away, but an angel of the Lord sent her back promising her that her descendants would be so numerous that the would not be countable. She had a son Ismael .