Onanist - Biblical Account

Biblical Account

After Onan's brother Er died, his father Judah told him to fulfill his duty as a brother-in-law to Tamar, by giving her offspring. Centuries later, in the days of Moses, this practice was formulated into a law of a levirate marriage, where the brother of the deceased would provide offspring to the childless widow to preserve the family line.

However, when Onan had sex with Tamar, he disregarded this principle when he withdrew before climax and "spilled his seed on the ground", since any child born would not legally be considered his heir. He disregarded the principle of a levirate union, so he died prematurely, exactly as God had warned would happen. (Genesis 38:3-10)