In The Hobbit, Bilbo and company met a group of stone trolls known as Tom, Bert, and William. Gandalf defeated these trolls by tricking them into staying in the clearing until the sun came out, when they turned to stone. In the beginning of The Lord of the Rings, Bilbo threw a big birthday party and invited Gandalf the Wizard and all of the hobbits in the Shire. Bilbo was telling a story to a group of children about the trolls that were going to eat them before turning to stone in the sunlight.
Stone trolls tend to be dumb and ill-tempered. Almost all stone-trolls have first names, and a few (like William Huggins) had last names. Stone trolls eat things such as wild fowl, wild pigs/boars, dwarves, hobbits, and fish (if they could actually catch them). They hunted simply by chasing or ambushing the animals, then hitting them with a weapon such as an axe or a club.
Stone-trolls commonly lived in caves or large burrows that went many yards underground, where they could shelter themselves from sunlight during the day. They slept on beds made of grasses and leaves or animal hides.
Stone-trolls participated in the War of Wrath, but they are not known to fight in any other wars. In the War of Wrath, they were used as beasts of burden and as shock troops, using giant axes and clubs to frighten their foes.
It is hard to say what the term "stone-troll" actually means because generally almost all trolls turn to stone when hit by sunlight. One possible meaning (as used in the book version of Fellowship of the Ring) is "any troll that has been turned to stone by the sun". Another possible meaning is that it is intended as an antonym for Olog-hai, since they do not ever turn to stone.
- During the scene when Frodo was stabbed with the Morgul-blade, the same trolls that Bilbo and the dwarves encountered in The Hobbit were in the background.