Denethor II was the twenty-sixth and last ruling steward of Gondor. During his early days Aragorn II worked as a soldier for him, under an alias, and won much fame, but Denethor realized soon that it was indeed Aragorn II and became scared and protective of his stewardship.
Denethor married Finduilas of Dol Amroth, who bore to him two children, Boromir and Faramir, yet died just over ten years after the marriage. Denethor became, then, very apprehensive of Sauron, and even used the Seeing-stone of Minas Tirith. Because of this Minas Tirith stood strong, yet Denenthor aged early and became very proud. When word came to the King of the death of his favorite son, Boromir, he tried to cremate himself and Faramir during the heart of the War of the Ring. Denethor did not succeed in burning his son, yet he did kill himself. It seems likely that before his death he looked into the Seeing-stone and saw the fleet of the Corsairs sailing up Anduin, not realizing that it was in truth commanded by Aragorn II.
Denethor was a good ruler, though he mistrusted Gandalf and thus deprived the city of a great counceller.