Trolls figure deeply in the history of the Cold Fens, and why they sit unexploited, edged only by small settlements with guards used to keeping oil and fire on hand.
What is known about trolls?
Besides what is in monster entries, not much.
They are a very odd thing, even in a magical world.
Trolls lack any positive feelings for non-trolls. There are trolls, there is food, and there are things that might be too difficult to kill and eat. They're utterly fearless, don't seem to reproduce in any normal fashion, and seem to lack seperate sexes. Periodically trolls show up in very large numbers. The recent "troll wars" were basically putting down an invasion of hundreds if not thousands of trolls into some areas around the Cold Fens. It's supposed they multiply by dismembering a troll and keeping the parts seperate so they'll grow into full trolls, but that's never been observed.
Trolls don't seem to have an organized religion, but it is believed by scholars that they worship a particularly loathsome troll god of some kind. Crude statues of a troll-like figure pockmarked with nail-made hokes have been found. Crude claw marks of varying sizes have been placed by trolls on menhirs and large boulders deep in their territory. Divinations have revealed the trolls refer to this being as the "Great Old One," "Great Destroyer," or "Troll Father." It's not clear if they respect or worship the "Troll Father" or just respect him. The idea of the trolls fearing such a being can be dismissed outright. Since trolls don't seem to age, it's not clear if this is some exception aging but immortal troll or a representation of a mythical "old" troll.
Trolls generally speak orcish, common, or other languages on the rare occasions that they speak. They have been seen to understand a very large number of languages, but just as often seem to understand nothing said to them. Especially evil wizards and evil clerics have been able to work with trolls - or magically suborn them - and seem to have no language issues in being understood. They are usually silent, and manage to coordinate with one another without seeming to directly communicate. Rumors of troll language that includes dozens of nuanced words for "bridge" and "goats" have never been substantiated.
Trolls have never been seen at play, or dancing, or creating art unrelated to the "Great Old One." It's possible they sing, if the hloo-hloo sounds they make can count.
That about sums up what is known about trolls.