Professor Quirrell is a fictional character from Harry Potter and the Philosopher's Stone. He was the Defence Against the Dark Arts teacher for years, but one year he took a year off to get some hands-on experience. It was rumoured he encountered vampires in the Black Forest. He had been acting jittery ever since his return.

According to the Harry Potter Lexicon, Quirrell's first name is Quirenius. There was no explanation of where this name came from, so it is currently in question. The Internet Movie Database lists Quirrell's first name as Slatero. The Harry Potter Trading Card Game: Diagon Alley lists Quirinus as his first name.

Quirrell was played by Ian Hart in the film.

Quirrell did indeed encounter something horrible when he traveled around the world: Lord Voldemort, who was barely alive. Voldemort twisted the young and gullible Quirrell into accepting the Dark way, and used him in a plan to steal the Philosopher's Stone (Sorcerer's Stone in America) from vault 713 in Gringotts Bank. Fortunately, Hagrid had removed the Stone from the vault earlier that same day to take it to Hogwarts.

Voldemort decided he would have to keep a closer watch on Quirrell, so he decided to share his body. To conceal the fact that Lord Voldemort's face was on the back of his head, Quirrel decided to wear a purple turban (note that in the movie, Quirrell is already wearing the turban in Diagon Alley).

After his return, Quirrell began acting jittery, most likely so that people wouldn't suspect him. He explained the turban by saying it was gift from an African prince for getting rid of a zombie. Even his First Year class didn't believe the story, as when he was asked how he got rid of the zombie, he went pink and started talking about the weather.

In order to keep Voldemort alive, he started killing unicorns in the Forbidden Forest and drinking their blood for Voldemort.

On Halloween Quirrell let a troll in as a diversion, and went to the third-floor corridor where the Stone was now hidden. Severus Snape, who already suspected Quirrell, went to the third floor in order to stop him. Snape was bitten by Fluffy.

In order to figure out how to get past Fluffy, Quirrell got Hagrid drunk, and gave him a dragon's egg. Quirrell sent a letter to Dumbledore, telling him to go to the Ministry of Magic; Quirrell used this as a diversion and went to get the Stone. However, he wasn't the only one: Harry and his friends Ron Weasley and Hermione Granger went after him (though they believed that it was Snape, not Quirrel, trying to steal the Stone).

Harry encounted Quirrell in the last chamber. There Harry discovered that Voldemort's face was on the back of Quirrell's head and in the ensuing struggle, Quirrell died, not being able to withstand Harry's touch, which burned him. Dumbledore said of this that Voldemort left as little mercy to his followers as his enemies.

"Quirrell" rhymes with squirrel, and also sounds similar to quarrel, meaning fight.