Stewardship becomes hereditary in Gondor (estimated date)
Event Type: Political
Age: 3rd Age - The Kings
The House of the Stewards was called the House of Húrin, for they were descendants of the Steward of King Minardil (1621-34), Húrin of Emyn Arnen, a man of high Númenórean race. After his day the kings had always chosen their stewards from among his descendants; and after the days of Pelendur the Stewardship became hereditary as a kingship, from father to son or nearest kin.
The Return of the King, LoTR Appendix A, Annals of the Kings and Rulers: Gondor and the Heirs of Anárion: The Stewards
In Gondor latterly... the office of Steward rose in importance and became hereditary, providing as it were a permanent "understudy" to the King, and an immediate viceroy at need....
Unfinished Tales, Part 4, Ch 3, The Palantíri
The date of this event, 1998, is from The Lord of the Rings, above. It appears that the dating of this event was changed from its original formulation in The History of Middle-earth, which says that though primogeniture was the practice since Pelendur (1945-98), it was not formalized until the Stewards, beginning with Mardil, became the de facto rulers of Gondor in 2050. I have used the date from a canonical source, but include the non-canonical quotes below as background.
Commentary by Elena Tiriel
Since [Eärnur's] death was not certain Mardil the Good Steward ruled Gondor in his name for many years....
For a long time before Mardil's day the Stewardship had usually been held by a member of his family (the Hurinionath, descended from Húrin, Steward to King Minardil). It now became hereditary like a kingship....
The Peoples of Middle-Earth, HoME Vol 12, Part 1, Ch 7, The Heirs of Elendil: The Southern Line of Gondor: The Anárioni
[Though] the Hurinionath were not in the direct line of descent from Elendil, they were ultimately of royal origin, and had in any case kept their blood more pure than most other families in the later ages. They were descended, father to son, from Húrin, Steward to King Minardil, who had laboured greatly for the ordering of the realm in the disastrous days of the plague.... From that time on the kings usually chose their steward from this family, though a son did not necessarily succeed a father. But in fact it had descended from father to son since Pelendur, Steward to [King Ondoher1], and after the ending of the kings it became hereditary, though if a Steward left no son, the office might pass in the female line, that is to his sister-son, or to his father's sister-son.
The choice was made according to their worth among the near kin by the Council of Gondor. But the Council had no power of choice if there was a son living.
The Peoples of Middle-Earth, HoME Vol 12, Part 1, Ch 7, The Heirs of Elendil: The Ruling Stewards of Gondor
The date is an estimate, based upon the event Pelendur, Steward to King Eärnil II, dies.
1 This text is from one of Tolkien's early drafts. For the sake of clarity, earlier versions of proper names used by Tolkien in this draft have been replaced with the versions in use in the canon sources. All substitutions are marked with brackets.
Elena Tiriel 11May05, 24Aug07