Before the foundation of Arnor there was already a sizable Númenórean population living in Eriador, a result of the slow emigration of Númenóreans which had started under Tar-Meneldur and Tar-Aldarion. The region was home to Middle Men of Edain stock, and the early colonists soon interbred with the indigenous population. The North-kingdom of Arnor had originally held the capital of High King Elendil the Tall at Annúminas, and the Dúnedain of that land were ruled for centuries by the descendants of Elendil's eldest son Isildur Elendilion.
After Isildur's death in T.A. 2, Arnor was ruled by his direct descendants, beginning with Valandil of Arnor, his youngest son. Before the end of the first millennium of the Third Age, the land of Arnor fell into dispute between the sons of King Eärendur , and the Dúnedain who lived there became divided into three realms: Arthedain, Cardolan and Rhudaur. One by one, these kingdoms fell to war, plague, and assaults by the witch-realm of Angmar, until at last the Dúnedain of Arnor had become a dwindled and wandering people known as the Rangers of the North.
Nonetheless, the line of Isildur was maintained through the Chieftains of this people. Aragorn Elessar was Isildur's Heir through thirty-nine generations, and it was he who reunited the Kingdoms of the Dúnedain after three thousand years of separation.
The Northern Dúnedain spoke a dark and mystical sounding dialect of northern Westron, sounding strange to outsiders.Their old Sindarin court-language had largely vanquished in the late third though many of their Scholars and Wise were still able to speak and read Sindarin, especially those families associated with the Elves of Rivendell.