Esrom was a son of Omer, a Jaredite king, born along with his brother Coriantumr and other siblings during the years Omer spent in captivity. Omer had been carried away captive by another of his sons, Jared, who had flattered many people, gained half the kingdom, and made war on his father (Ether 8:2-4).
Esrom and Coriantumr, angered by Jared’s actions, raised an army and gave battle to him by night. They destroyed Jared’s army and were about to kill him as well, but Jared pled for his life and offered to give up the kingdom to their father. They granted him his life, restoring the kingdom to Omer (Ether 8:5-6).