In the Book of Mormon, Coriantumr (/kɔːr.iːˈæn.tə.mɜːr/) is the name of three figures that appear throughout the book's narrative. Chronologically, these three are: one of the sons of Omer, a deposed Jaredite king later restored to his throne by his sons Esrom and Coriantumr; the last of the Jaredite kings, who lived to see his people destroyed and to see another people live in the land; and a Nephite dissenter, who was made leader by the Lamanites over the Lamanite armies.
The first Coriantumr (chronologically) was one of the sons of Omer. Omer had been deposed from his throne by his son Jared, who kept him imprisoned. Esrom and Coriantumr had been born while their father was held as a prisoner by Jared. Coriantumr and Esrom restored their father as the king of the Jaredites twice. (See Omer (Book of Mormon) for more details.)
Coriantumr was one of the last Jaredites, as well as one of their last kings. In his reign, Ether came under the direction of God to prophesy to the people, and could not be restrained. Accordingly, his prophecies were great and marvelous, and nobody believed because "they saw them not." Eventually, he was cast out, the prophecy of their destruction was given, and Ether remained in a cave, recording the events.
Accordingly, Coriantumr was troubled in the same year Ether was cast out with a great war among the people. Many rose up who were mighty men and sought to destroy him, "by their secret plans of wickedness." However, Coriantumr, being well-studied in war and other cunning learning, gave battle unto them. Neither he nor his house repented; neither did the house of Cohor and Corihor. The war took a turn for the bloodiest, and the king was wounded. Ether came to him and told him that the Lord would spare him and his household if they would repent; otherwise, they would be destroyed and another people would inherit the land and Coriantumr would be the last survivor to see them inherit the land.