Q: Could Anyone Have Become a King in Middle-earth?
ANSWER: The great royal families of the Elves, Dwarves, and Dunedain all appear to have been chosen/annointed by the Valar in some way. The Valar chose three Elven ambassadors who later became the kings of the Vanyar, Noldor, and Sindar (and Olwë, brother of ambassador Elwë, became king of the Falmari). From these royal families came the first ennobled Edainic families: the Marachians, Bëorians, and Haladin. And from the Marachians came the Kings of Numenor (and through a “daughter line” the Kings of Arnor and Gondor).
But there are other kings, even among the Elves, who apparently were never granted authority by the Valar. Denethor was the King of the Laegrim (“Green-elves”) of Ossiriand, for example; and in the Second Age “Sindarin adventurers” established kingdoms among the Silvan Elves in eastern Middle-earth. Tempting though it might be to associate Thranduil and his family with Elwë’s house, Tolkien never made a clear, explicit connection. Cirdan is said to be related to Elwë but even Cirdan’s authority seems to have been arranged or enhanced by the Valar through his relationship with Ossë and Ulmo.
Among men the family line that eventually became the Kings of Rohan were descended from the “self-styled king” Vidugavia; and there were other such kings, including Bard I of Dale (whose “election” as king by at least some of the people of Esgaroth may represent how these “self-styled kings” came to power).
In ancient Germanic tradition most tribes would only accept kings from certain “noble” families, but any man from those families could become king if he had sufficient support. There is no record of how these noble families achieved their status; any legends attempting to explain such origins were recorded centuries after the fact. Tolkien’s kingly houses appear to follow this tradition, even among the Elves.
Of course, we know nothing of the dynasties among the Easterlings and Southrons. A few kings are mentioned, such as the renegade descendants of Castamir the Usurper who established a kingdom in Umbar — but they at least could claim descent from Anarion and thus Numenor’s nobility. The only Orc dynasty is the line of Azog, whose son Bolg led the Orcs in the Battle of Five Armies. King Golfimbul led the Orcs at the Battle of Greenfields.
# # #
Have you read our other Tolkien and Middle-earth Questions and Answers articles?
Most likely your view that anyone who was ,,elected” or otherwise appointed by people could become a king is correct. This is hinted in words spoken by Theoden that in case his dynasty died out without heir people of Rohan would choose new king.
,,Behold! I go forth, and it seems like to be my last riding,” said Théoden. “I have no child. Théodred my son is slain. I name Éomer my sister-son to be my heir. If neither of us return, then choose a new lord as you will.”