In the first book of the Harry Potter series, "Harry Potter and the Philosopher's Stone" (or "Harry Potter and the Sorcerer's Stone" in the United States), Professor Quirrell releases a troll into the dungeon of Hogwarts School of Witchcraft and Wizardry. It was part of a scheme orchestrated by the main antagonist, Lord Voldemort, who was attached to the back of Quirrell's head. Quirrell's goal was to create a distraction and draw attention away from his attempts to steal the Philosopher's Stone, which was hidden within the school.