Trolls

    The word Troll is a translation of Sindarin Torog, according to the Return of the King Appendix F "Of Other Races".

    Trolls were made as a mockery of the ents, so they were large and strong. Their great early weakness was turning to stone in the light of the sun. In the Hobbit and later in the Fellowship , hobbits encountered trolls after entering the Trollshaws, which was a great forest east of Rivendell containing the ruins of the Dunedain castles of Arnor. Since the wars with the Witch-King, the area became the home of traveler-eating trolls such as William Huggins, Bert and Tom, who were tricked into remaining in the open until sunrise by Gandalf, rescuing Thorin, Bilbo, and company.
    Sauron bred these trolls up to greater cunning and, by breeding or training, improved their skill with weapons for the War of the Ring. The new type, given to bellowing in a fight, were known as the hill-trolls of Gorgoroth.

    Notes about the nature of trolls are from the Hobbit and  Lord of the Rings:
Origin:

    Trolls (as they are called in the English edition, Throlls in the Danish) are shown to turn to stone in daylight because of their origin in the Hobbit, "Roast Mutton". Narration says, "...trolls, as you probably know, must be underground before dawn, or they go back to the stuff of the mountains they are made of, and never move again..."
    This passage could suggest that the Flame Imperishable from Eru was placed into stone creations, the way the dwarves were made by Aule and given life later by Eru. Perhaps Aule, pleased with the dwarves and wanting to try living beings again after the Children of Iluvatar were awakened, made these out of stone. They may have been corrupted later after Aule turned to other things. More likely this coming from stone is only a hobbit tale, although it comes from the narrator.

    Early trolls were dull and lumpish with no more language than beasts. (RotK App F "Of Other Races")
 
First troll breeding program:

    Trolls being a "mockery of ents" has been referred to a number of times. This is found in the Lord of the Rings' Two Towers , "Treebeard" chapter shortly after the ents sing their war song "To Isengard". Treebeard explains to Merry and Pippin how strong an ent is, by comparison with trolls:

    "You do not know, perhaps, how strong we are. Maybe you have heard of Trolls? They are mighty strong. But Trolls are only counterfeits, made by the Enemy in the Great Darkness, in mockery of Ents, as Orcs were of Elves. We are stronger than Trolls. We are made of the bones of the earth...."

 Life style:

    Hobbit, "Roast Mutton": Gandalf met two elves from Rivendell in a hurry to avoid the trolls, telling Gandalf that the three trolls had come down from the mountains and settled in the woods near the road, waylaying strangers and scaring people out of the district. The trolls had a cave hidden by bushes, with a stone door requiring William's key. Trolls looted anything: brass buttons, clothes, coins. Glamdring, Orcrist, Sting were in their stash. Although having such weapons, the trolls used fists and branches against each other, and trapped the unsuspecting dwarves by luring them with a camp with food and hiding in the bushes to catch them in sacks. The trolls spoke as humans of low education. They cooked and wore clothes and boots. They had ale, bread, cheese, and bacon. They understood things like stockings and using sacks. The troll's purse had an alarm system, calling out when Bilbo tried to steal it. They used names later which are usually associated with humans. Would that be because they were conveniently short, humans were related, or in mockery of certain humans that trolls had met?
   Hobbit, "A Short Rest": Trolls also made swords, since Elrond said the looted swords weren't troll-make but probably stolen. (He also said Glamdring, Orcrist, Sting were from Gondolin made for the goblin wars, that they were probably plundered by dragons or goblins. Glamdring once belonged to the king of Gondolin.)

Relationship with dwarves:

    "Trolls simply detest the very sight of dwarves (uncooked)." This suggests an old troll/dwarf quarrel, possibly while in the mountains which both groups seem to reside in. Perhaps it was a rivalry over Aule's attention or an argument about whether to listen to Aule or Melkor and Sauron.

Newest variety of Troll:

    Fellowship, "Shadow of the Past". "Trolls were abroad, no longer dull-witted, but cunning and armed with dreadful weapons."
    Here we have the intervention of Sauron and his breeding programs. He took the old troll and bred for battle. Trolls were already large and strong, so perhaps they were crossed with humans for intelligence. Humans were readily available to Sauron and he did not require consent. 
    Fellowship, "Bridge of Khazad-dum". In the corridor outside the Chamber of Mazarbul, Gandalf sees one or more cave-trolls among the many Moria Orcs and the few Mordor Orcs, so they were associated.  "A great cave-troll, I think, or more than one."  Boromir closed and wedged the door. Something much larger than an Orc comes at the door, which can only be a cave-troll, certainly too big and strong for an Orc, scaly, and possibly wrong-colored as Orcs are said to be swart or black: 

    "There was a blow on the door that made it quiver; and then it began to grind slowly open, driving back the wedges. A huge arm and shoulder, with a dark skin of greenish scales, was thrust through the widening gap. Then a great, flat, toeless foot was forced through below. There was a dead silence outside.
    Boromir leaped forward and hewed at the arm with all his might, but his sword rang, glanced aside, and fell from his shaken hand. The blade was notched.
    Suddenly, and to his own surprise, Frodo felt a hot wrath blaze up in his heart. "The Shire!" he cried and sprang beside Boromir, he stooped, and stabbed with Sting at the hideous foot. There was  a bellow, and the foot jerked back, nearly wrenching Sting from Frodo's arm. Black drops dripped from the blade and smoked on the floor."

    After the door is again slammed shut, the Orcs need rams and other tools to beat it open again. Apparently their cave-troll no longer aided them. The black troll blood smoked on the floor, but it may have smoked from contact with Sting of Westernesse. This thing, this troll, is huge. It has dark skin covered with greenish scales that can turn the blade of the Stewards' heir, certainly a fine blade but having no magic as Sting did. The troll's foot is flat and toeless.

    Return of the King, "Black Gate Opens": The orcs were mired in the mud of the pools during the battle.

    "But through them (orcs) there came striding up, roaring like beasts, a great company of hill-trolls out of Gorgoroth. Taller and broader than men they were, and they were clad only in close-fitting mesh of horny scales, or maybe that was their hideous hide; but they bore round bucklers huge and black and wielded heavy hammers in their knotted hands. Reckless they sprang into the pools and waded across, bellowing as they came."

    They like to bite throats of victims, such as the attempt on Beregond. They have black blood which is not human red, as Pippin discovered when he killed the troll chieftain to rescue Beregond.

    Return of the King  Appendix F "Of Other Races":
    Sauron found the original dull, lumpish Trolls with no more language than beasts and made use of them. He taught them what little they could learn and increased their wits with wickedness. Then the Trolls learned what language they could from the Orcs. In the Westlands, the Stone-trolls spoke debased Common Speech. But at the end of the Third Age a new troll-race appeared in southern Mirkwood and the mountain borders of Mordor, called Olog-hai in the Black Speech.
    Olog-hai were without doubt bred by Sauron, but the stock was unknown. They were in fashion of body and mind unlike even the largest Orcs, far surpassing them in size and power. These had been filled with the evil will of their master, being fell, strong, agile, fierce, and cunning, but harder than stone. "Unlike the old race of the Twilight, they could endure the Sun as long as the will of Sauron held sway over them. They spoke little, and the only tongue that they knew was the Black Speech of Barad-dur."

    Summary description:

    Taller and broader and stronger than an Orc or Man. Greenish. Scaly. The foot is flat and toeless. Cave and hill-trolls bellow and have black blood. Hill trolls use round bucklers and war hammers.
    Types mentioned:
    Earliest before being used by Sauron: dull and lumpish, with no more language than beasts.
    Early Sauron-improved, dull-witted trolls, but able to make and use swords; cave-trolls; hill-trolls. Spoke a little as their small minds could handle, as they learned some Orcish or Common Speech from the Orcs.
    Olog-hai, bred up by Sauron: cunning, agile, stronger and larger than the the largest Orc, and stone-hard, speaking only Black Speech.