http://lotr.wikia.com/wiki/Aranarth

Aranarth was born in TA 1938 to Arvedui and Fíriel. In his youth, the Witch-king of Angmar was at the height of its power and destroyed the Northern Kingdom, overrunning its capital city Fornost. Most of the surviving people, including Aranarth, fled to Lindon, but King Arvedui went north to the Ice-Bay of Forochel. Aranarth urged Círdan to send ships to rescue Arvedui, but this ship never returned. It was later learned that the ship had sunk with Arvedui on board as well as the Palantiri of the north.[3]

By right, this made Aranarth now King of Arnor, but since that was lost he could not claim the title. Aranarth rode with the army of Gondor under Eärnur and saw the destruction of Angmar. Aranarth's people became known as the Rangers of the North (or Dúnedain), and he was the first of their Chieftains who dwelt in the wilds of in Eriador. In time, their origins were generally forgotten by the common people of Arnor.[4]

While the Rangers defended Arnor from the remnants of Angmar's evil, the Wizard Gandalf went to Dol Guldur, and drove out Sauron the Necromancer. Thus began the period known as the Watchful Peace, a time where attacks by the enemy were few and far between. Aranarth's son Arahael was born in Rivendell, and was given a name with the Kingly prefix of Ar(a)-, to signify that by right he would be King of Arnor.

Arahael succeeded his father at his death in TA 2106.[2]