Quirinus Quirrell is the Defence Against the Dark Arts teacher at Hogwarts during Harry Potter's first year. Prior to his employment at Hogwarts, he is said by Rubeus Hagrid to have had a "brilliant mind", and was a fine teacher while studying from books; some time before Harry's arrival at Hogwarts, "he took a year off to get some first-hand experience". Rowling stated in a live web chat on 30 July 2007 that Quirrell had worked at Hogwarts as Muggle Studies teacher for a certain length of time, before taking the cursed Defence Against the Dark Arts position in the same year that Harry joined. Upon his return, he appears perpetually nervous and has developed a stutter and nervous ticks. Quirrell's attire includes a new purple turban which he claims to have received as a reward from an African prince for getting rid of a zombie.
Harry first meets Quirrell at the Leaky Cauldron, while being escorted by Hagrid to Diagon Alley to shop for school supplies. Quirrell is next seen at Hogwarts conversing with Snape at the start-of-term banquet, and then regularly while teaching Defence Against the Dark Arts lessons. During the school's Halloween banquet, Quirrell appears in the Great Hall to warn staff and students of a troll in the dungeons and then he faints. While playing Quidditch, Harry is almost thrown off his broom by some sort of curse and he, Ron, and Hermione believe it is Snape who is responsible. They begin to suspect that Snape is on a mission from Voldemort to steal the Philosopher's Stone hidden in a secret chamber in Hogwarts; however, when Harry finally arrives in the chamber, he discovers that it is not Snape, but Quirrell, who is the real villain. Quirrell then reveals that he was the one who let in the troll and muttered the curse to attempt to throw Harry off his broom. During the climax of the story, as Harry and Quirrell try to recover the stone from the Mirror of Erised, Voldemort reveals himself on the back of Quirrell's head, formerly concealed by the turban, and speaks directly to Harry, threatening to kill him if he does not assist Voldemort in recovering it. After Harry refuses, Voldemort orders Quirrell to attack Harry, who holds off Quirrell long enough for aid to arrive, at which point Voldemort flees, in his non-physical form. Voldemort's departure, as well as the agony suffered by him because of his contact with Harry, who continues to be protected by the love of his mother and the spell that was cast by her sacrificing her life to save Harry, causes Quirrell to die.
It is later revealed in the chapter The Prince's Tale from Harry Potter and the Deathly Hallows [HP7] that Snape was actually keeping an eye on Quirrell under Dumbledore's orders.