Aragorn's claim to the throne of Arnor can be traced through the tables of the Rangers, Kings of Arthedain & Kings of Arnor. His position as heir to the throne of Arnor is straightforward, for the line is unbroken back to Elendil, the founder and first ruler of the Northern Numenorean 'exile' kingdom. Although Isildur, Elendil's elder son, was first joint King of Gondor, he was on his way to take up the throne of Arnor when ambushed and slain following the death of his father, Elendil. By the time Anduril is reforged for Aragorn, Arnor had of course long since ceased to exist as a kingdom. There are also no other claimants, the lines of the kings of Rhudaur & Cardolan having failed.

Aragorn's claim to the throne of Gondor is less obvious. It rests upon his claim to be the rightful Heir of Isildur, and upon the right of Isildur's Line to claim the throne.

Isildur's departure from Gondor to take up the throne of Arnor following the death of his father, Elendil The Tall, left the throne in the hands of Anarion (his younger brother). From then on the royal lines of both kingdoms effectively split into the Northern and Southern Dunedain. The distinction is made clear by the argument over the throne of Gondor which arose after the marriage of the last Arnorian king, Arvedui of Arthedain, to Firiel, daughter of Ondoher (the 31st king of Gondor). On the death of Ondoher and his sons, Arvedui believed this gave him sufficient reason to claim the throne of Gondor. The claim was rejected by the Council of Gondor, who chose Earnil (a descendant of king Telumehtar). In the event, Arvedui could not pursue his case at the time.

[ Whether Arvedui's claim was valid is a matter for loremasters; it was based upon an interpretation of the traditions of Numenor. It had been laid down early on in Numenor that the throne could not pass down a female line - Silmarien, daughter of the 4th king of Numenor, was barred from becoming Queen on these grounds (see the Kings of Numenor). The law was later changed to allow eldest daughters to become Queens, however, causing discontent in the 'rightful' male descendents of Elros. ]

Neverthless, Aragorn is the sole direct male descendent of the Line of Elendil. Moreover, Isildur did not renounce the throne of Gondor, which he held jointly with his brother. The Southern Kingdom was originally divided into two, with Isildur based at Minas Ithil in Ithilien and Anarion at Minas Anor; the building of its capital at Osgiliath in the middle of the River Anduin was a compromise, albeit one which in practical terms could only serve as the demarcation point between the two parts whilst both brothers were present.

Whatever their exact kinship, kings of Numenor had to be of the Line of Elros. The bloodline of Elendil (and therefore Aragorn) connects to the Line of Elros via the Lords of Andunie. The Lords ruled a western province of Numenor which kept faith with the Elves and the Valar, while the main ruling line wavered and eventually turned away from the Elves, jealous of their immortality and close connections with the Blessed Realm. The name Elendil means 'Elf-friend' and it was his father, Amandil ('friend of Aman'), who foresaw the downfall of Numenor and made secret preparations to separate and if possible save the persecuted Faithful from the consequences of turning against Aman and the Gods.

The Lords of Andunie traced their line back to Valandil (the first Lord of Andunie) who was the son of Silmarien (daughter of Tar-Elendil) and Elatan, a nobleman of Andunie. The line through Lady Silmarien goes back to Elros, 1st King of Numenor.

Elros himself was of the House of Hador / Folk of Marach, one of the three Tribes of Men who entered the now lost region of Beleriand in the First Age and made friends with the Elves there. It was thus the same House from which Elrond and his daughter Arwen are descended (see Elrond's Ancestry). Aragorn's blood has distant traces of the other two Tribes of Men, and the Noldor. (See also the Note on Ancestry).