Quirrell was the Defence Against the Dark Arts teacher at Hogwarts during Harry's first year. In reality, he was working for Voldemort, who was sharing his body at the time (visible on the back of Quirrell's head).
"A foolish young man I was then, full of ridiculous ideas about good and evil. Lord Voldemort showed me how wrong I was." ~ Quirrell
Quirrell was a teacher of Muggle Studies before taking the post of Defence Against the Dark Arts. He took a year off to get some practical experience (presumably of Defence rather than Muggle Studies) where his encounters with vampires and a hag supposedly left him a nervous wreck with a stutter. However, this was an act devised to conceal his new loyalties to Lord Voldmort. He secretly worked for him from then on, his new master leading him into such crimes as breaking into Gringotts, repeatedly attempting to murder a child, and the slaying a unicorn in order to drink its blood. His attempt to steal the Philosopher's Stone from Hogwarts led to his being caught by a surprised Harry. There he dropped his nervous act and revealed his true loyalties, but his failure to get the Stone and to kill Harry again before Albus Dumbledore arrived ultimately led to his death. Voldemort abandoned him just before this.
Portrayals Within Films
Quirrell always wore a turban in order to conceal the fact that Voldemort was in the back of his head.
Magical Accomplishments and Skills
- Quirrell owned a turban which he claims was given to him by an African prince for getting rid of a troublesome zombie. It smelt of garlic and he used it to conceal Voldemort's face in the back of his head.