Onan
The second son of Judah. When his elder brother Er died childless, Judah told him to perform the duty of a brother-in-law and raise up offspring for him — but knowing the child would not be counted as his own, he spilled his seed on the ground whenever he went in to Tamar. What he did was wicked in the sight of the Lord, and he died. His refusal is what drives Tamar to the deception at Enaim that follows.
What we know — and how we know it
Where in scripture
GenesisNumbers1 ChroniclesShe conceived again, and bore a son; and she named him Onan.
Genesis 38:4
Judah said to Onan, “Go in to your brother’s wife, and perform the duty of a husband’s brother to her, and raise up offspring for your brother.”
Genesis 38:8
Onan knew that the offspring wouldn’t be his; and when he went in to his brother’s wife, he spilled it on the ground, lest he should give offspring to his brother.
Genesis 38:9 — Refuses his duty
The sons of Judah: Er, Onan, Shelah, Perez, and Zerah; but Er and Onan died in the land of Canaan. The sons of Perez were Hezron and Hamul.
Genesis 46:12
The sons of Judah: Er and Onan. Er and Onan died in the land of Canaan.
Numbers 26:19
The sons of Judah: Er, Onan, and Shelah; which three were born to him of Shua’s daughter the Canaanitess. Er, Judah’s firstborn, was wicked in Yahweh’s sight; and he killed him.
1 Chronicles 2:3
Scripture quotations are from the World English Bible, a public-domain translation.