Arnor was a kingdom ruled by Men after Númenor fell.
It fell thousands of years later and the line to the throne went into hiding, renaming themselves, the Dúnedain, or the Rangers of the North.
The last of that line is Aragorn, son of Arathorn II.
The rulers of Arnor also ruled Gondor.
The Dúnedain are descended from Elros, Elrond’s brother. Although they are both Half-Elven, and Elrond chose an immortal life, Elros chose to live a mortal life. But because of how far down the family tree the current Dúnedain rangers are, they don’t life AS long. Although, they still have a life span of about 200 years.