Mathonihah was one of the twelve disciples Jesus Christ chose to minister to the Nephites after his resurrection. He is named once, in the list of those disciples, where he appears as the brother of Mathoni (3 Nephi 19:4). The record gives no further detail about his life.
As one of the twelve, he was among those Jesus gave power and authority to baptize and told the multitude to heed (3 Nephi 12:1). When Jesus later asked the disciples one by one what they desired of him after he returned to the Father, nine asked that their ministry might end at the age of man so they could come to him in his kingdom; Jesus told them they would come to him at seventy-two years old and find rest with him (3 Nephi 28:1-3).