Argeleb I (S. "Silver King") succeeded his father, Malvegil, as the seventh King of Arthedain in T.A. 1349 at an age of 123. As the royal line had died out in both Cardolan and Rhudaur at this time, he was the first king to reclaim sovereignty over all three northern kingdoms, taking the royal prefix "Ar-" as a token of this in his name. He was both an accomplished scholar and a fine fighter. His reign marked the beginning of Arthedain's claim to Cardolan and Rhudaur. When Argeleb ascended the throne in Fornost, no heirs of Isildur remained in either other state, and Angmar controlled Rhudaur. So, Argeleb declared himself to be the seventeenth King of all Arnor, aggravating many of the petty Princes in Cardolan and sparking a war with the Witch-king as he was contested by both Rhudaur and Angmar.
A great builder of fortresses and castles, the Arthadan king fortified his frontiers and erected towers atop the Weather Hills, but he was slain in battle by warriors from Rhudaur in T.A. 1356 in battle against his united enemies. He was succeeded by his son Arveleg I having ruled for only seven years.