Onan (Hebrew: אונן, ʼŌnān; "Name means::strong") (Born::Abib 2267 AM—Died::Tammuz 2281 AM) was the second-born son of Judah by an unknown Canaanitish woman.
Onan's older brother Er had married Tamar, behaved wickedly, and died at the hand of God. So Judah ordered Onan to marry Tamar and engender a son, to satisfy the levirate obligation to her. Onan did not want to do this, so he practiced a form of contraception that involved withdrawing from the woman to prevent fertilization. For this God put him to death as well. (Genesis 38:8-10 )
Onan's wicked act was an act of fraud against his wife, and demonstrates one evil of self-gratification: the disconnection of the sexual act from its intended purpose, hence an interruption of the divinely-ordained order.