Onan was a figure detailed in the Book of Genesis chapter 38, as the second son of Judah who married the daughter of Shuah the Canaanite. Onan had an older brother Er and a younger brother, Shelah as well. After being commanded by his father, Judah, to procreate with the late Er's wife Tamar, Onan instead "spilled his seed on the ground whenever he went in" because "the offspring would not be his", and was thus put to death by Yahweh. This act is detailed as retribution for being "displeasing in the sight of Lord".

The story of Onan has varying interpretations, being viewed as a cautionary tale against coitus interruptus and masturbation. Other analysts claim he was killed for refusing his father's command to continue the tribe's lineage.