Trolls
They are essentially sentient rocks (though don't ever use the "r" word): enormous, mobile, of humanoid shape, with intelligence and personality. And of igneous, metamorphic, and sedimentary varieties.
Trolls have interesting seams of valuable minerals as their blood vessels and nervous system. This phenomenon has at least two repercussions. One: a troll's brain, silicon-based, will overheat and slow down in Ankh-Morpork, and the troll will become sadly stupid; the brain will also overheat in strong sun, causing trolls to stop moving in daylight. Two: when a troll has stopped moving while their brain has overheated in daylight, this troll will look just like a lump of rock, with interesting seams of valuable minerals, and may be (and have been) attacked by mining dwarfs. This is very likely the initial cause of the animosity between trolls and dwarfs, even though, after hundreds of years, the feud goes on because it is a cultural tradition for both species. It being a cultural tradition does not mean it is nice; trolls and dwarfs have repeated the Battle of Koom Valley several times. Historic casualties are high. The hostility lives on and is found in any place with a significant number of both species, for example, Ankh-Morpork; serious riots have occurred in Men at Arms and Thud!.
Neither have Trolls gotten on well with humans, through most of history. Not being able to digest carbon-based life forms didn't stop them from eating them, and a belt of human skulls used to be a popular fashion statement among male Trolls. Naturally, this sort of thing led to retaliation and a lot of derogatory bedtime stories. Nowadays, relations are much more peaceful all around, and the game of Aargrooha has nearly disappeared. Trolls retain a fear and loathing of billy-goats, however. It's something like elephants and mice.
Trolls are large and powerful, but have never been a political force to be reckoned with in their home mountains (where it is nice and cold and trolls are clever), except for warring against the dwarfs. Trolls generally come from the Ramtops or Überwald. In the Ramtops, trolls are considered a nuisance; in Überwald, trolls are either enemies of dwarfs or treated as semi-sentient slaves (see The Fifth Elephant). In Bonk, Überwald, trolls are considered properties and need to carry a passport signed by their owners. Only in Ankh-Morpork have trolls been able to influence some policies by being a large immigrant group. They have a rather inefficient crime syndicate called the Breccia, led by the troll Chrysoprase, who is the fastest in assimilating into the city human society. Trolls have also organized the Silicon Anti-Defamation League to improve the image of trolls in the cities.
Trolls have teeth of diamond. A troll dentist might also be a rich diamond merchant. A troll gangster might wear the teeth of their former enemies as jewelry. While most trolls are capable of growing diamond teeth (and possibly regenerating fresh diamond, just as rodents' teeth continually grow from underneath to replace what is ground away on the top?) this is as far as it goes for most trolls. But just once in a while, trollish genetics throws up a Diamond Troll made entirely of diamond. Such a being is naturally super-intelligent as they can regulate their own bodily temperature - evidenced by the thin layer of frost on the outside that also serves as protection against the glare for onlookers.
Diamond Trolls, by custom and precedent, generally gravitate to the position of High King or equivalent over the whole of Trolldom. However, the current incumbent didn't want the kingship if it meant a resumption of large-scale warfare between trolls and dwarfs, but reserved a right to step into his inheritance when circumstances improved. Until pivotal developments in Koom Valley made peace feasible, Mr. Shine was content to remain incognito in Ankh-Morpork, teaching Thud and working for greater understanding between Trolls and Dwarfs. Now, with the troll clans united under his leadership, trolls' interests have found their champion in international politics, as exemplified by Vetinari's cooperation in efforts to eradicate the Crystal Slam trade worldwide.
Female Trolls
Female Trolls can generally be identified in that they have a tendency to look like sculptures of stone-age goddesses of fertility. Nonetheless, like male trolls, they usually wear little more than a loincloth. Since trolls minimise on clothing to try to stay cool, reverse logic dictates that the more a troll wears, the more erotic it is. Nanny Ogg mentioned that females wearing clothes excites males, and that there is a club in Ankh-Morpork where the troll dancers end up wearing seven layers of heavy sheets.
It used to be that troll courtship consisted of a male troll asking a father's permission to hit the female on the head with a nice rock, then, after the female had recovered from her mild concussion, and approved the rock, they would enjoy a nice candle-lit human for two (although that's not done anymore, at least if there's any chance of getting caught), and then for the rest of her life, the female troll will be home subduing whatever prey that the male brings home for dinner. But after coming to Ankh-Morpork and witnessing human and dwarfish courtship rituals, some are taking a more feminist approach and choosing their own rocks to hit their own males over the head, without needing to ask their father's permission. (Moving Pictures).
Female trolls use distinctly female names (names of precious or semi-precious stones). In some regions, male trolls expect female trolls to polish, and it's not encouraged for them to grow lichen (a la a woman shaving), since "bald is modest" (Monstrous Regiment). In cosmopolitan Ankh-Morpork, on the other hand, Mr Stronginthearm's troll beauty products includes a spray guaranteed to grow lichen for that "almost clothed" look.
Troll Afterlife
While trolls almost certainly have souls, it is unknown what happens to them when they die. While Death has come for many humans, dwarves, dogs and even a golem in the course of the discworld books, he has never yet been seen to collect the soul of a troll. Then again, most of them don´t actually die, as explained upon below.
For the trolls themselves they apparently believe they are moving backwards through time as they refer to the 'sunset of time' rather than the 'dawn of time' (they can see the past, so it must be "ahead of," not behind, them). While a troll can die from injuries, they do not die of old age. A really old troll will generally find a nice quite place in the mountains and sit and think. This will go on for years, and as their thoughts get deeper their synaptic processes get gradually slower. Eventually they stop altogether (perhaps because they have reached the conclusion) and the troll is no more than rock. One troll this almost happened to was Old Grandad, but he was rudely woken by some short-lived thugs who had lit a fire in his mouth.
Trolls becoming dormant like this has also been another source of tension between the dwarf and troll races. Dwarfs like to mine rocks with interesting minerals in them, and a dormant troll is basically a large rock made of interesting minerals. This has led to ' unpleasantness' when some dwarf miner is attacked by a troll he's just put his pick into, or a troll discovering that the stone slabs of that fireplace have been made out of their granny.
Language
Most Trolls can speak the language of humans, but they have their own language and written script as well. They also have an older language known as 'Old Troll' spoken several hundred years ago but still understood by trolls alive today such as Detritus & Mr. Shine.
Troll Graffiti is a common sight in Ankh-Morpork, rather than paint on the walls, the troll just pushes their finger into the plaster and makes the words in the side of the building. You can tell how important the message is by how deep it has gone in.
For a complete list of trollish phrases click here
Troll Drink and Drugs
Trolls are as prone to intoxication as any other sentient species. The intoxicants and their delivery systems are unique to a silicon-based life-form. Such things as troll cigarettes have been referenced. These have a lot in common with fireworks. Trolls have been known to get addicted to fireworks. Troll drinks range from molten sulphur, delivered in a suitably ceramic drinking vessel, to the Electrick Floorbanger or luglarr. Sam Vimes has learnt to use this to his advantage in a riot-control situation. Hard drugs - and troll drugs are the hardest on the Disc - are a different problem. Slab and Slide are a persistent problem among the young, and Crystal Slam is outright lethal, although any suggestion that Chrysoprase is involved will be very firmly denied by the Silicon Anti-Defamation League. Many things can be social drugs to trolls. In Unseen Academicals, we meet Concrete, a troll who has hit on the opiate uses of iron filings.