In the Book of Mormon, the brother of Jared is the most prominent person in the account given in the beginning (chapters 1–6) of the Book of Ether. Moriancumer (/mɔːr.iː.ˈæn.kə.mɜːr/) is the name of the place where Jared and the people he was traveling with (later to be called Jaredites) settled for a time. Some years after the publication of the Book of Mormon, Joseph Smith was residing in Kirtland, Ohio when Reynolds Cahoon had a son. One day when Smith was passing his door, Cahoon called him in and asked Smith to bless and name the baby. Smith did so and gave the boy the name of Mahonri Moriancumer. When Smith finished the blessing, he laid the child on the bed told Cahoon that the "name I have given your son is the name of the brother of Jared; the Lord has just shown [or revealed] it to me." William F. Cahoon heard Smith make this statement to his father; and this was the first time the name of the brother of Jared was known in the church in this dispensation” (George Reynolds, “The Jaredites,” Juvenile Instructor, 1 May 1892, 282).
According to the Book of Ether, Jared and his brother were present at the Tower of Babel. When the language of the people was confounded, Jared asked his brother to ask God not to confound their own language, that of their friends, and that of their immediate families.
After being granted to have their language not confounded, they asked to be led to where the Lord would have them go, hoping that it would be a choice land. They were led through the wilderness, across many waters, to the "great sea which divides the lands", and then dwelt in tents at the seashore for four years. They named this place where they had (temporarily) settled Moriancumer. The account relates that after four years, the Lord came to the brother of Jared and "chastened him because he remembered not to call upon the name of the Lord."