Denethor, son of Rķan the younger sister of the previous Steward Dior, succeeded his uncle at his death in T.A. 2435 and inherited a generally peaceful realm. However, an end came to this when Ithilien was suddenly attacked by fierce Orcs of an unknown kind: the Uruk-hai. Ithilien was lost and its people were slain or fled to other lands of Gondor.
He had three children: first two daughters, then a son.
He was followed by his only son Boromir at his death in 2477.
As a result, Denethor refused to trust Thorongil's advice, Gandalf in particular whom Thorongil was a strong supporter of, and Denethor hardened his heart when he discovered that Thorongil was really of Isildur's line, the legitimate but powerless heir of Arnor and Gondor.
Denethor ordered Gondor's forces to the outer defences of Osgiliath and the Rammas Echor, wanting to make a stand since they had been built at great expense and not yet been overrun.
Denethor was a shrewd and insightful man, and he apparently discovered that Thorongil was in fact Aragorn, the Chieftain of the Dunedain of the North, and as such one who could stake a claim to the throne of Gondor.
Denethor was opposed to yielding the rule of Gondor to the heir of the lost kingdom of Arnor.
Denethor was strong-willed, and he was initially able to maintain control of the Anor-stone and prevent Sauron from forcing his gaze to the Ithil-stone.