Aranarth was a Dunadan and the first Chieftain of the Dunedain of the North. He was the elder son of Arvedui who was the last King of Arthedain. Aranarth would have become King of Arthedain, had the Witch-king not ravaged the kingdom.
When the Kingdom was destroyed, Aranarth fled to Lindon, but his father fled to the North. Cirdan learned of this and sent a ship to recover Arvedui, but it never returned.
Later, it was found that the ship HAD found Arvedui, but it was lost in the icy seas.
Aranarth took charge of the Dunedain of the north, but took the title of Chieftain since his kingdom was destroyed.
He was succeeded by his son, Arahael.