Quirinus Quirrell's first mountain troll

Quirinus Quirrell's first mountain troll was a male mountain troll brought into Hogwarts School of Witchcraft and Wizardry on Hallowe'en of 1991 by Quirinus Quirrell, possessed by Tom Marvolo Riddle, in an attempt to steal the Philosopher's Stone of Nicolas Flamel.

Quirinus Quirrell was able to control this troll, a rare talent. He said later that he had a gift with trolls. He even used a troll to help protect the Philosopher's Stone.

Background
At the beginning of the holiday, the first year Charms class were to practise the Levitation Charm. Professor Filius Flitwick told them to use the incantation Wingardium Leviosa.

Later, that day, Ron Weasley hurt the feelings of Hermione Granger by remarking that she had no friends. She was later seen crying in the girls' bathroom by Parvati Patil.

The Halloween Feast
"Troll in the dungeons! Troll in the dungeons! Thought you ought to know."

- Quirinus Quirrell, distracting the Great Hall

As the students were attending the Hallowe'en Feast, Professor Quirrell ran into the Great Hall "warning" them of a troll in the dungeons, which he had in fact deliberatley let in as a distraction.

Headmaster Albus Dumbledore told the prefects to take the students back to their dormitories and for all teachers to follow him to the dungeon. During the walk back to the Gryffindor Dormatories, Harry remembered Hermione was unaware of this.

Attack in the Girls' Bathroom
Harry and Ron ran toward the bathroom and spotted Severus Snape, following Quirrell to the third floor corridor. They, unknowingly, locked the troll in with Hermione. Realising their mistake, they ran in and Ron screamed at it and threw something at it. Harry, meanwhile, jumped on the troll and shoved his wand up its nose. The troll grabbed and Ron hovered the troll's club over its head and knocked it out. This was the start of Harry and Ron's friendship with Hermione. It is unknown what happened to the troll.

Aftermath
Harry, Ron, and Hermione originally assumed that Snape was behind the "troll business", but Harry, trying to stop Voldemort in his attempt to steal the Philosopher's Stone, found out that it was Quirrell, not Snape, who had let the troll in.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Philosopher's Stone (video game)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince (video game)
 * LEGO Harry Potter: Building the Magical World
 * LEGO Harry Potter: Characters of the Magical World
 * LEGO Harry Potter: Years 1-4
 * Pottermore
 * Harry Potter Trading Card Game
 * Harry Potter LEGO Sets