Shelah was the third son of Judah and his Canaanite wife Bat-Shua. He is known from Genesis as one of Judah's sons, but died young without leaving offspring, and his role is connected to the levirate marriage where his brother Onan's duty was to raise up an heir for Er, the firstborn.
After Er and Onan died, Judah promised his daughter-in-law Tamar that Shelah would become her husband when he grew old enough, but Judah feared that Shelah might also die.
11Then Judah said to his daughter-in-law Tamar, "Live as a widow in your father's house until my son Shelah is grown up." For he thought, "He may die too, like his brothers." So Tamar went and settled in her father's house.
14So she took off her widow's clothes, covered herself with a veil and wrapped herself up, and sat down at the entrance to Enaim, on the road to Timnah. For she saw that although Shelah was grown up, she had not been given to him as his wife.
3The sons of Judah: Er, Onan, and Shelah. These three were born to him by Bath-shua the Canaanite. Er, Judah's firstborn, was evil in the LORD's sight, and the LORD put him to death.