Jacob was a Zoramite who commanded the Lamanite army holding the Nephite city of Mulek during the war of the twenty-eighth year of the judges. When Moroni, Teancum, and the Nephite chief captains sent embassies asking him to bring his army out to fight on the plains between the cities, Jacob would not come out. Unable to meet them on open ground, Moroni sent Teancum with a small number of men down near the seashore; when the Lamanite guards reported Teancum, Jacob’s army marched out against him, and Teancum retreated northward, leading them in pursuit. While they chased him, Moroni took Mulek with part of his army (Alma 52:20-24).
Jacob, described as having “an unconquerable spirit,” led the Lamanites back “with exceeding fury” against Moroni, determined to cut his way through to Mulek, but Moroni’s men did not give way (Alma 52:33-34). They fought with many slain on both sides; Moroni was wounded and Jacob was killed (Alma 52:35).