1 Chronicles 2:3

The sons of Judah
The genealogy begins with him, though the fourth son of Jacob; because, as Kimchi says, this book treats chiefly of the kings of Judah; but rather not only because Jesse and David sprang from him, but also the King Messiah:

Er, and Onan, and Shelah, which three were born unto him of the
daughter of Shua the Canaanitess;
see ( Genesis 38:2 Genesis 38:12 ) ,

and Er, the firstborn of Judah, was evil in the sight of the Lord;
because he did that which was evil:

and he slew him;
he died by the immediate hand of God, and so his brother Onan, being wicked also, ( Genesis 38:7 Genesis 38:10 ) .