Professor Quirinus Quirrell was a wizard and the Defence Against the Dark Arts professor at Hogwarts School of Witchcraft and Wizardry during the 1991-1992 school year. Prior to this, he served as the professor of Muggle Studies. While appearing timid and harmless, Quirrell was secretly in servitude to Lord Voldemort, whose disembodied spirit had possessed him and lived on the back of his head, concealed by a large turban. As Voldemort's host, Quirrell's primary mission was to steal the Philosopher's Stone to restore his master to a physical body, making him the primary antagonist of Harry Potter's first year.
Before his corruption by Lord Voldemort, Professor Quirrell taught Muggle Studies at Hogwarts. He took a year-long sabbatical to gain practical experience before taking up the famously cursed Defence Against the Dark Arts teaching post. During his travels, he journeyed to the forests of Albania, where he encountered the weakened, spectral form of Lord Voldemort. Possessing a theoretical interest in the Dark Arts and a desire for recognition, Quirrell was no match for Voldemort, who overpowered and possessed him. Upon returning to Hogwarts, Quirrell became a vessel for Voldemort's will. On 31 July 1991, he attempted to steal the Philosopher's Stone from Vault 713 at Gringotts Wizarding Bank but discovered that Rubeus Hagrid had emptied it earlier that day. Throughout the school year, he made several attempts to get past the protections guarding the Stone at Hogwarts. On Hallowe'en, he let a mountain troll into the dungeons as a diversion, hoping to get past Fluffy, the three-headed dog guarding the trapdoor. During Harry Potter's first Quidditch match, Quirrell attempted to murder Harry by jinxing his broomstick, but was thwarted by a counter-curse from Severus Snape and a fire set by Hermione Granger. Quirrell's final attempt occurred at the end of the school year. He managed to overcome the various enchantments protecting the Stone, but was unable to retrieve it from the Mirror of Erised. He was confronted by Harry Potter in the final chamber. Voldemort, speaking from the back of Quirrell's head, ordered him to kill Harry. However, Quirrell was unable to touch Harry's skin without suffering excruciating pain, as Harry was protected by the lingering magic of his mother, Lily Potter's, sacrificial love. When Quirrell made direct contact, his body began to burn and blister. Voldemort's spirit fled the dying body, leaving Quirrell to perish.
Quirrell was described as a pale young man who perpetually twitched and stuttered. This nervous disposition was largely an affectation to prevent others from suspecting him. His most defining feature was a large, purple turban that he claimed was a gift from an African prince as a reward for dealing with a troublesome zombie. He also told students it was packed with garlic to ward off a vampire he had met in Romania. In reality, the turban served to conceal the horrifying face of Lord Voldemort on the back of his head. Publicly, Quirrell presented himself as a timid, stuttering, and easily flustered academic who was afraid of his own subject and even his students. His true personality was far more cunning and ruthless. He possessed a deep-seated ambition and a dangerous curiosity for the Dark Arts, which ultimately led to his downfall. While he served Voldemort, he was ultimately a weak-willed individual, easily dominated and controlled by his master.