Trolls in Tolkien's Lord of the Rings books are large, strong, but dim-witted, evil creatures who served the Dark Lords Morgoth and Sauron. Different types of Trolls appear, with some turning to stone in sunlight, while others, like the Olog-hai, are smarter and more resistant to sunlight.
 

Trolls were likely created by Morgoth in mockery of the Ents, similar to how Orcs were created by deforming Elves.​ Trolls have limited intellect and communicate through grunts or a "debased form of the Common Speech". There were five main types of Trolls during the 3rd Age.​​

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The oldest race of Trolls are the Stone Trolls. They were large and strong, but lumpish and the least intelligent of the Trolls and have a habit of using great hammers. They are vicious and storm into battle bellowing and are known to bite their enemies. If they enter any sunlight they would be turned to stone. Notable encounters include the three Stone Trolls Tom, Bert and William Huggins, who were tricked by Gandalf to stay out in the sun and turned to stone.

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Cave Trolls are a race of Trolls that dwelt in caves. The Fellowship of the Ring encountered one in Moria, where it was involved in a battle at the Bridge of Khazad-dûm. They too were less intelligent and had green scaled skins. They would also turn to stone if entering sunlight.

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Mountain Trolls are large, strong but unintelligent. They have a brownish hue to their skin, but can walk in daylight without any issues.

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Hill Trolls of Gorgoroth, are large and have a pale skin. They are less intelligent, but can stand to walk in daylight without any issues. They live in hill and moorland areas.​

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Olog-hai Trolls were bred by Sauron and are a more cunning and smarter breed of Troll that appeared towards the end of the Third Age and could withstand sunlight. They speak only the Black Speech of Mordor and their body is covered in dark scales. They are strong, agile and fierce.

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