In The Hobbit they speak with very thick Cockney accents. They turn to stone when exposed to sunlight and they enjoy eating meat (such as mutton, hobbits and Dwarves) and drinking beer. While threatening, the trolls in The Hobbit serve as a comic element. They even have normal names: Tom, Bert and William (Bill) Huggins (the only one with a given surname). The fallen Vala and first Dark Lord, Morgoth, created the first Trolls before the First Age. They were strong and vicious, but stupid creatures. The major weakness of at least some Trolls was that they turned to stone in sunlight. Nobody knows how he managed to breed them, though it is stated by Treebeard of the Ents that Trolls were "made in mockery of" them, as Orcs were of Elves, though not necessarily from Entish stock. However, they are likely a corrupted form of some other race of Middle-earth, as neither Morgoth nor Sauron have access to the Secret Fire, and cannot therefore create things; only corrupt that which already exists. There is reference that sunlight will return them to the stone from which they were made in The Hobbit and The Lord of the Rings.
During the wars of Beleriand, Gothmog, the Lord of Balrogs, had a bodyguard of Trolls. While leading his men in a final stand to protect the retreat of Turgon and the continued secrecy of the Kingdom of Gondolin, the great warrior Húrin faced them, and due to Morgoth's emphatic orders to have Húrin captured alive, he managed to wipe them out. Their apparently caustic blood, however, melted his axe, allowing orcs to swarm over him and bind him, his capture ending the Nírnaeth Arnoediad, the Battle of Unnumbered Tears, where Morgoth seemingly triumphed over the united armies of Elves, Men and Dwarves.
Many Trolls died in the War of Wrath, but some survived and joined the forces of Sauron, the greatest surviving servant of Morgoth. In the Second Age and Third Age, Trolls were among Sauron's most dangerous warriors.
Tolkien used several different terms for types of trolls, though there seems to have been some overlap in meanings;
In the film The Lord of the Rings: The Two Towers, when Frodo and Sam approach the Black Gate to see an army of Southrons enter, the doors are opened and closed by shackled Trolls, which are perhaps similar to the Mountain-trolls that manned the battering ram Grond. During the Battle of the Pelennor Fields there is a reference to "men like half-trolls", also called troll-men, but it is unclear whether these men actually had some trollish ancestry or were simply compared to trolls (for some readers, the first interpretation is supported by the similar and interchangeable terms "orc-men" and "half-orcs", referring to crossbreeds of Saruman).
In Peter Jackson's 2001 The Lord of the Rings: The Fellowship of the Ring, there is also only one cave-troll. Boromir first sights it; it later barges through the open doors, and smashes much of the Chamber, including Balin's tomb, in the ensuing fight. It stabs Frodo, who is saved by his mithril shirt (in the book it is an Uruk captain who spears him). It is killed by the members of the Fellowship (though it puts up a good fight), who spear and hack at it until Legolas dispatches it with an arrow. It enters the soft palate of its mouth and goes straight through its brain, emerging from the top of its head after becoming stuck in the thick skull.
Battle Trolls were shown as the shock troops in the motion pictures The Lord of the Rings: The Two Towers (film) and The Lord of the Rings: The Return of the King, sporting armour and spiked clubs alluded to in the appendices. They were then used in the Siege of Gondor as primary shock troops after the gates of Minas Tirith were broken. At least one survived and is seen later, attempting to break down a gate.
Sauron's military used other trolls for moving extremely heavy objects such as gates and siege towers, sometimes chaining them. The cave-troll in Moria wore a collar with a trailing chain, suggesting it may have been a former labourer, though this particular specimen was undisciplined enough to attack some of its own allies in the fight thus perhaps showing others' need to restrain it.
Aragorn fights one of the Olog-hai during the battle of the Black Gate. This Olog's entire upper body is covered in black plated-armour, making it more menacing. While most trolls in the movies wielded clubs, this one wielded a sword, as well a briefly seen mace.
In the world of the films, mountain-trolls, including the cave-trolls of Moria, are about 17 feet (5 m) tall, with massive limbs, potbellies, and dark scales on its back and shoulders. They come in stony colours, with the most common being grey. They have 22 teeth, including two fangs on the lower canines. As in the book, their blood is black, and is so hot that when split, it sizzles on the floor. They are mainly carnivorous, but can digest plant matter if need be. The eyes are either grey or blue. They wear loincloths of leather that they find in the Mines or are given by the Goblins. They sometimes roar when in a battle rage, but are incapable of forming words or language. They often wield either a great club or a hammer. Cave-trolls are usually found with small groups of Orcs. They are too unintelligent to hunt food for themselves, often consuming whatever hapless creature they come across, so food is an advantage they get from working with the Orcs. Their fingernails extend to most of their fingers, and were allegedly used to dig holes into the rock itself.
The Olog-hai differ from the other Trolls depicted in the New Line movies in that they have more forward-facing eyes as well as hair on their bodies, suggesting that they are a more advanced form of Troll. They are usually grey to black in colour. Mountain trolls and Olog-hai have much in common, they are both much larger and more intelligent than most trolls and more resistant to light. However Olog-hai are certainly far superior to Mountain trolls in all these aspects.
Forest trolls were invented for the EA game version of The Lord of the Rings: The Two Towers. They have hard grey skin, are resistant to arrow fire, and carry a large quiver of wood logs (to use as firewood and projectiles), as well as a mace like a cave troll.
For the game version of The Lord of the Rings: The Return of the King, trolls also returned as enemy units. Although they were slow, their attacks couldn't be blocked and were very strong, but there was often a war pike around that made them easy to kill. They also appeared as enemies in "Lord of the Rings: The Third Age". In this game, they were also slow but powerful, and could take a lot of damage before dying. Some of the later trolls in the game (these were called attack trolls) wielded a pair of large swords, while a stronger kind carried massive war hammers. Trolls also appear as controllable units in The Lord of the Rings: The Battle for Middle-earth, its sequel, The Lord of the Rings: The Battle for Middle-earth II and its expansion The Rise of the Witch-king. In The Lord of the Rings: The Battle for Middle-earth, it is necessary for a regular mountain troll to gain a rank (after destroying enemy units, etc.), to become an attack troll where it gains an armour bonus and can heal by itself as the only non-hero unit who is able to do so. In The Battle for Middle-earth II, attack trolls can be made from a Rank 3 Troll Cage. In The Rise of the Witch-king, the Angmar faction has a troll hero named Rogash. In all the Battle for Middle Earth games, Trolls are depicted as "tank" units (slow, very strong, can take massive damage before being killed).
Wood Trolls in the MMO The Lord of the Rings Online Trolls that appear to be semi-entish made of wood appear in the Trollshaws, they are particularly difficult to kill and deal a lot of damage.