Tom Bombadil:

Tom Bombadil is a bit of an enigma. From what he says of himself, he is probably a Maia. He is a bit strange, but very jolly and friendly. He certainly saved the hobbits lives at least twice: once with Old Man Willow, and with the Barrow-wight. It could be argued that with the gift of the swords from the Barrow, he saved their lives at least once more.

Thranduil:

Thranduil was the king of the Elves of Mirkwood. He founded the kingdom around the year 1000 of the Third Age. Prior to this, he lived in Lindon. There is no information on when he left Middle-Earth, but there are records of his kingdom lasting into the Fourth Age. Thranduil was an able battle commander who fought in both the Battle of the Five Armies and the War of the Ring that we know of, and probably others as well.

Thorin Oakenshield:

The leader of the Dwarves on the quest for Smaugs treasure, Thorin Oakenshield was the grandson of the King under the Mountain. He fought in the Dwarf and Goblin Wars which ended at the east Gate of Moria. There he gained the name Oakenshield.

Like many Dwarves, Thorin was somewhat grasping of treasure. Though there was much treasure under the Mountain, when Smaug was killed, he would not give up even the treasure that had belonged to the Dalemen. This started the Battle of the Five Armies, as is recorded in Bilbo's diary, called The Hobbit. By the end of the Battle of the Five Armies, when it included the Eagles, Goblins, Elves, Men and Dwarves, Thorin was dead, as were his cousins Fíli and Kíli.

Théoden:

The King of Rohan, Théoden had been under the influence of one of Saruman's spies, for many years, until the coming of Gandalf the White, during the War of the Ring. Gandalf revealed the traitor in King Théoden's court, and brought hope back to the King of the Mark. Théoden, at Gandalf's advice, sent a host of Riders to Helms Deep where they managed to defeat Saruman's army with the aid of the Huorns. After this, Théoden was present at Isengard when Gandalf removed Saruman from both the Istari and the Council. About a week later, Théoden led the host of the Rohirrim to Gondor, where he fell in battle on the Pelennor Field, and died after naming Éomer the next king of the Rohirrim.

Tuor:

One of the three known unions between Men and Elves was made by Tuor and Idril. Tuor was a Man, the son of Huor, who was chosen to warn Turgon, the King of Gondolin of impending doom. Though Turgon ignored the warning, Tuor was high in his favours, even to the point of marrying his daughter. Tuor escaped the fall of Gondolin, along with Idril, his son, Eärendil and many trustworthy lords of Gondolin. Though it is not known for sure, many believe that Tuor was counted among the Elves, as he and Idril built a ship and sailed into the West.

Túrin:

The son of Hurín, Túrin was fostered in Doriath at the request of Morwen, his mother. As at this time, Túrin's father was a captive of Morgoth, there was almost a curse on him. Certainly most of what he did turned to evil.

Unintentionaly, Túrin killed one of Thingol's advisors, then thinking himself outlawed, he spent several years with an outlaw band. Beleg the elf rescued Túrin after he had been caught by orcs, though while cutting the bonds about Túrin, Beleg accidentally wounded him with his sword. Believing that he was being tortured by orcs, Túrin unthinkingly killed Beleg.

After this he wandered to many places, eventually remaining in Narogthrond. There he convinced the elves, who had long defended by stealth to build a bridge and attack in force. This lead both to the abandonment of Narogthrond, and to much more misfortune for Túrin, when the dragon Glaurung came. The bridge allowed him to cross the river and attack Narogthrond. There he bespelled Túrin to abandon the one who could have aborted much misfortune for him, Finduilas, the daughter of Orodreth their king. The dragon later bespelled his sister Nienor. She was found later by the woodsmen who had taken in Túrin as their leader. Unknowing, the two married.

About a year later, Glaurung the dragon, was known to be passing near and Túrin determined to slay the beast. This he did, and was later found and thought to be dead. Nienor, his sister came by to be sure and found that he was not. The dragon, still alive broke the spell on her and told her who she really was. In despair she threw herself off the cliff. Túrin, also realizing the wrongs he had done, threw himself on his sword, and so died.

Turgon:

Born in Aman, Turgon joined the flight to Middle-Earth. When he found a securely hidden location he began the building of Gondolin, which took seven years. For several hundred years, Turgon remained hidden, bringing his forces out only once in the Nirnaeth Arnoediad, where he and his men's retreat was shielded by Hurín and Huor, protecting it from the eyes of Morgoth. After this he never came forth in open battle again. Warned by Ulmo, through Tuor, of the coming doom, Turgon chose to ignore the warning. He died in the fall of Gondolin to the forces of Morgoth.

Telchar:

The dwarven smith who forged both the Narsil and Angrist in the First Age of the Sun.

Théodred:

The only child and the heir of King Théoden. Théodred was killed in the Battle of the Fords of Isen, where the Rohirrim were fighting the orcs of Saruman.

Tulkas:

The last-come of the Valar, Tulkas wed Nessa, the sister of Oromë. He delights it contests of strength, and has a strong hatred of Morgoth.

Thingol:

One of the three Elves who traveled to the Undying Lands to see the Two Trees and to lead his people there. While the other two, Inwë and Finwë returned to Aman, Thingol, originally named Elwë did not, falling in love with the Maia, Melian and remaining in Beleriand. Many of his people, the Teleri remained with him.

With Melian, he ruled the realm of Doriath through the remaining Ages of the Stars, and much of the First Age of the Sun. He had one daughter, Lúthien, who fell in love with the mortal, Beren. Thingol, in an attempt to deny the two marriage, sent Beren after one of the three Silmarils. When the Silmaril was given to Thingol, he had it set in the Nauglamir. The dwarves doing the work were jealous and killed Thingol in an attempt to take the necklace.

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