Denethor II:

The Steward Denethor II was the last of the Ruling Stewards of Gondor. He ruled Gondor in the years of the War of the Ring, though he did not live to see victory. Denethor was born in the year 2395 of the Third Age of the Sun. After the death of his wife, Finduilas, it is believed that Denethor started to use the Palantir of Minas Anor. It was through this that he gained news of Sauron's strength, though it also destroyed his mind with despair. Denethor burned himself alive in the madness of despair.

Damrod:

One of the two guards that Faramir left with Frodo and Sam in Ithilien. The other was Mablung.

Dernhelm:

The name used by Éowyn when she rode in disguise to the Battle of the Pelennor Fields. At the same time she carried Meriadoc Brandybuck against the orders of King Théoden. She revealed her true name when she challenged the Witch-King.

Drogo Baggins:

Drogo Baggins was the father of Frodo Baggins and the husband of Primula Brandybuck. He was drowned in an accident on the Brandywine River in the year 2980.

Dain Ironfoot:

Dain became the king of the Lonely Mountain after the death of Thorin in the Battle of the Five Armies, and was still able to fight in the War of the Ring (There were sieges in the area of the Lonely Mountain) at over two hundred years old. He died in the final days of the War of the Ring.

Dwalin:

One of the twelve Dwarves who accompanied Thorin in the quest for Smaug's treasure. He survived the Battle of the Five Armies. No date was given for his death.

Dori:

One of the twelve Dwarves who accompanied Thorin in the quest for Smaug's treasure. He survived the Battle of the Five Armies. No date given for his death.

Dior Eluchíl:

Dior was the son of Lúthien Tinúviel and Beren. Among his children was Elwing, who helped Eärendil in his quest to ask the Valar for aid. Eventually, Dior was the ruler in Mengroth. There he was slain by Celegorm, Curufin and Caranthir, as he was in posession of the silmaril regained by his father, Beren. However, before he died, he was able to kill the three sons of Fëanor.

Déagol:

After Isildur's death the One Ring fell into the Anduin River. Almost twenty-five hundred years later, Déagol found the ring when fishing with Sméagol in the regions of the Gladden Fields. Sméagol demanded it as a birthday present, and on Déagol's refusal, he murdered him, taking the Ring for his own. Déagol's body was never found.

Déagol was of hobbit origins, specifically from the Stoor branch, as was explained by Gandalf and recorded in the Red Book of Westmarch.

Daeron:

One of the elves of Doriath, Daeron was considered to be the greatest of the minstrels in Middle-Earth. Though he loved Lúthien, the daughter of King Thingol, she did not love him in return. Because of his love, he twice betrayed her to her father. First, when she had first met Beren, and the second time, when she had gone to Daeron for help in rescuing Beren from the dungeons of Sauron.

One of the other deeds for which Daeron was remembered was the creation of the Cirth, a series of runes for inscriptions. These were used mainly by the Dwarves at least until the end of the Third Age. On seeing them in the Book of Mazarbul, Gandalf called the runes 'Daeron's Runes'.

Daeron became the best minstrel out of love for Lúthien, composing music for her to dance and sing to.

When Lúthien left Doriath in search of Beren, Daeron went searching for her. However, he never found her and ended up wandering into the Eastern regions of Middle-Earth, where for ages afterwards, he composed laments in her name. Nothing is known of when or if he died.

The Lord of the Rings
The Silmarillion
The Hobbit
The Complete Guide to Middle Earth by Robert Foster