None of them were stated. So the answer would be **none**. If there were any, they would have challenged the rule of the Stewards prior to Aragorn's arrival (26 of them). The last of the 'official' line of the Kings of Gondor was Earnur. > Eärnur had held the crown only seven years when the Lord of Morgul repeated his challenge, taunting the king that to the faint heart of his youth he had now added the weakness of age. Then Mardil could no longer restrain him, and he rode with a small escort of knights to the gate of Minas Morgul. None of that riding were ever heard of again. It was believed in Gondor that the faithless enemy had trapped the king, and that he had died in torment in Minas Morgul; but since there were no witnesses of his death, Mardil the Good Steward ruled Gondor in his name for many years. Thus, it follows as such that no other descendant challenged the Stewards for the throne. Mentioned here: > Now the descendants of the kings had become few. Their numbers had been greatly diminished in the Kin-strife; whereas since that time the kings had become jealous and watchful of those near akin. Often those on whom suspicion fell had fled to Umbar and there joined the rebels; while others had renounced their lineage and taken wives not of Numenorean blood. Also stated was: > So it was that no claimant to the crown could be found who was of **pure blood**, or whose **claim all would allow**.. Hence, by the time of the War of the Ring, little to no descendant could claim their right to the Kingship. Some of the Dunedain of the South *could* be likely candidates, but it is never fully stated of their exact lineages. ---------- In the North, there were the Dunedain of the North and (unique to the North) a chieftain of the Dunedain, who is Aragorn. The chieftains were descended directly from Aranarth, who is descended from Isildur and from him Elendil. It is stated that Dirhael, Aragorn's maternal grandfather, is a descendant of Aranarth. >His son Arathorn sought in marriage Gilraen the Fair, daughter of Dirhael, who was himself a descendant of Aranarth. He would've been eligible for a claim but he never tried. He'd probably get denied, though, as he wouldn't be in favor of the Dunedain of the South. So, overall, there would be none who could claim the Kingship of Gondor save Aragorn or his descendants. Tolkien never stated any other eligible person.