Dior (Steward of Gondor)
Dior's grandfather Hador was the last of the Stewards to enjoy a truly long life, and he ruled Gondor for one hundred and seventeen years. This meant that his son Barahir, and his grandson Dior, both came late to the Stewardship and ruled for only a brief time. Dior was the last Steward to enjoy an untroubled rule, as his heir Denethor would see the breaking of the Watchful Peace and the beginning of centuries of warfare.
Dior is remarkable as the only recorded Ruling Steward to leave no direct heir. In volume XII of The History of Middle-earth we're told that he had no children of his own, and was succeeded therefore by the son of his sister Rían. This seems to be borne out by the Appendices to The Lord of the Rings, which state that Gondor's Stewardship became '...hereditary as a kingship, from father to son or nearest kin.' (Appendix A iv The Stewards, our italics). This reference to 'nearest kin' seems intended to refer specifically to Dior.
Dior ruled as Steward for twenty-three years, and seems to have been succeeded by his nephew Denethor I.