- "It was a horrible sight. Twelve feet tall, its skin was a dull, granite grey, its great lumpy body like a boulder with its small bald head perched on top like a coconut. It had short legs thick as tree trunks with flat, horny feet. The smell coming from it was incredible. It was holding a huge wooden club, which dragged along the floor because its arms were so long."
- — Harry Potter and Ronald Weasley witness a Troll for their first time on Hallowe'en[src]
The Troll in the Bathroom was a mountain troll, brought into Hogwarts School of Witchcraft and Wizardry on 31 October (Hallowe'en) 1991 by Quirinus Quirrell, then possessed by Lord Voldemort, in an attempt to steal the Philosopher's Stone of Nicolas Flamel.
- Hermione: "You're saying it wrong. It's Wing-gar-dium Levi-o-sa, make the gar nice and long."
- Ron: "You do it, then, if you're so clever"
- — Hermione and Ron arguing during Charms class[src]
On 31 October (Hallowe'en) 1991, the first year Charms class were taught how to perform the Levitation Charm (Wingardium Leviosa) by Professor Filius Flitwick. All the students in the class struggled with its pronunciation, apart from Hermione Granger, who lectured Ron Weasley on his incorrect casting and cast it perfectly herself, much to Flitwick's delight.
After class, a particularly annoyed Ron insulted Hermione Granger to his friend Harry Potter by remarking that she was a "nightmare" had no friends due to her bossy and boastful nature. Hermione overheard this, and was later seen crying in the girls' bathroom by Parvati Patil, while Neville Longbottom reported this to an unknowing Harry and Ron.
The Hallowe'en Feast
- "Troll -- in the dungeons -- thought you ought to know."
- — Quirrell distracting Hogwarts school[src]
As the students were attending the Hallowe'en Feast, Professor Quirrell suddenly sprinted into the Great Hall frantically with a terrified expression over to the teacher's table, warning Albus Dumbledore of a troll that had been let into the dungeons before collapsing on the floor.
The whole student body then began to panic in an uproar, with Headmaster Albus Dumbledore having to first silence them all with Purple Firecrackers before telling the Prefects to take the students back to their dormitories and for all teachers to follow him to the dungeon to deal with the loose troll. During the walk back to the Gryffindor Common Room, Harry Potter remembered Hermione was unaware of this, and he and Ron subsequently went to rescue Hermione.
Attack in the Girls' Bathroom
- "Hermione had sunk to the floor in fright; Ron pulled out his own wand -- not knowing what he was going to do he heard himself cry the first spell that came into his head: "Wingardium Leviosa!" The club flew suddenly out of the troll's hand, rose high, high up into the air, turned slowly over -- and dropped, with a sickening crack, onto its owner's head. The troll swayed on the spot and then fell flat on its face, with a thud that made the whole room tremble."
- — Ron having defeated the Troll with the Levitation Charm[src]
Harry and Ron ran toward the bathroom and spotted Severus Snape, following Quirrell to the third floor corridor. They then noticed the troll lurking about the corridor and unknowingly locked the troll in the girls bathroom with Hermione. Realising their mistake, they ran in to rescue a terrified Hermione. Ron throwing a metal pipe at it, which, along with all the shouting, aggravated it. Harry, meanwhile, jumped on the troll and shoved his wand up its nose in an attempt to stop it. This caused the troll to howl in pain and it began to swing its club. With Harry's life in danger, Ron ingeniously thought of the first spell that came to his head, the Levitation Charm, which he had learnt earlier that day, and cast it to levitate the troll's club. He then dropped the club on top of its head, knocking it out instantly and causing it to fall to the ground incapacitated.
- "Well, I still say you were lucky, but not many first years could have taken on a full-grown mountain troll. You each win Gryffindor five points. Professor Dumbledore will be informed of this. You may go."
- — McGonagall rewarding Ron and Harry for having defeated the troll[src]
After the troll fell the floor, Harry observed that it was only knocked out, not dead. Harry extracted his wand from the troll's nostrils, with it being covered in Troll bogeys, much to his disgust. Then, Professors Minerva McGonagall, Snape and Quirrell entered the bathroom to witness the aftermath of the pandemonium. A horrified McGonagall questioned the boys as to what they were doing going after a fully grown mountain troll, but Hermione lied to McGonagall, claiming she had sought the troll out herself. McGonagall then lectured the three first years on their recklessness, deducted five points from Gryffindor from Hermione for being foolish, gave Ron and Harry five each for having defeated the troll, and sent them away to the Gryffindor Common Room. Afterwards, Harry, Ron and Hermione became best friends, forming the "trio".
- Harry: "You let the troll in?"
- Quirrell: "Certainly. I have a special gift with trolls, -- you must have seen what I did to the one in the chamber back there? Unfortunately, while everyone else was running around looking for it, Snape, who already suspected me, went straight to the third floor to head me off -- and not only did my troll fail to beat you to death, that three-headed dog didn't even manage to bite Snape's leg off properly"
- — Quirrell revealing his deception to Harry Potter in the Underground Chambers[src]
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.
Behind the scenes
- In the PS1 and PC versions of the Philosopher's Stone video game, when dealing with the troll, Harry must cast the Knockback Jinx to destroy pieces of debris the troll throws at him, while Ron charms the club with the Levitation Charm. In the console versions, the troll must be defeated the Softening Charm, by having the troll hit enchanted Spongify tiles, which will cause its club to bounce back and strike it head, which must be done five times to knock it out. There is also a major plot difference in the game, where they rescue Hermione from the second-floor girls bathroom when it should be the first floor.
- Harry Potter and the Philosopher's Stone (First appearance)
- 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) (Mentioned only)
- Harry Potter and the Half-Blood Prince (video game) (Mentioned only)
- LEGO Harry Potter
- LEGO Harry Potter: Building the Magical World
- LEGO Harry Potter: Characters of the Magical World
- LEGO Harry Potter: Years 1-4
- Wizarding World
- Harry Potter Trading Card Game
- Harry Potter: The Creature Vault
- Harry Potter: Puzzles & Spells
- Harry Potter: Magic Awakened (Appears on a spell card or during spell introduction)
- Harry Potter: The Wand Collection (Mentioned only)