Coriantumr was the last King over the Jaredites in "all the land." That is, Moron and adjacent countries. His parentage is not given in the genealogy of Ether in Chapter 1. In the Book of Omni (vv. 20-22), it is related that a large engraved stone was brought to King Mosiah in Zarahemla. On this stone was an account concerning Coriantumr. He had wandered southward, after the Battle of Ramah, and reached Zarahemla, where he lived nine months (moons). He had, presumably, prepared the record on the stone that was brought to King Mosiah for translation.
Ether was a "descendant" of Coriantor. (Ether 11:25) Coriantor was the legal king. His name, therefore, appears in the genealogy notwithstanding he was held in captivity. Coriantumr must have been an usurper, holding and wielding illegal authority.
In the days of this unrighteous ruler, the Spirit of the Lord came upon Ether and called him to the prophetic office. His special mission was to preach repentance. As Jonah was sent to Nineveh, or Jeremiah to Judah, to warn of disaster unless the people repented, so Ether was sent to the Jaredites, and so faithfully did he discharge his mission that he cried repentance "from the morning, even until the going down of the sun." It was a tremendous mission, if he was the only missionary at work to make the whole nation conscious of the fact that wickedness would end in destruction, and that repentance, alone, would bring Salvation. Ether also taught that hope and faith "make an anchor to the souls of men." In other words, that through them, men feel safe even when furious hurricanes hurl destructive waves against their frail crafts. At such times faith is the chain that connects the ship with the firm anchorage. The storms, no matter how terrifying, are only on the surface; the divine anchorage is always safe.