Quirrell was portrayed on the big screen by Ian Hart.
Before taking up his position at Hogwarts as Defence Against the Dark Arts professor, Quirrell travelled the world on a year-long sabbatical, supposedly to gain first-hand experience of interacting with Muggle society. In truth, however, he was curious about the supposedly-dead Lord Voldemort, believing him to still be alive in some form and wished to learn about the Dark Arts from him, all to satisfy a life-long need to make others acknowledge him.During his travels, Quirrell did indeed find the Dark Lord, or rather, what was left of him. Even in a weakened state, Voldemort still possessed greater magical power than Quirrell and was able to subdue him and when he realised that Quirinus had a position at Hogwarts, Voldemort used his charisma to manipulate Quirrell to serve him.
In 1991, after returning to Britain to take up his new position at Hogwarts, Quirrell was instructed by Voldemort to acquire the legendary Philosopher's Stone, an artifact supposedly capable of granting its bearer immortality. He had attempted to steal it from Gringott's Wizarding Bank, but the Stone had been removed from its vault before he could reach it. To ensure that Quirrell would not fail again, Voldemort took possession of Quirrell's body, binding himself to his servant and appearing as a sinister face growing out the back of Quirrell's head. From then on, Quirrell hid Voldemort's face by constantly wearing a turban.
During the school term, Quirrell sought out the hiding place of the Philosopher's Stone within the walls of Hogwarts Castle. To divert the attention of the faculty and students, he allowed a troll to enter the castle on Halloween night, using the opportunity to sneak into the restricted Third Floor Corridor where the Stone was being hidden. Severus Snape, who suspected Quirrell, followed him, and was bitten by the three-headed dog Fluffy in the process of trying to head Quirrell off.
Later in the year, Quirrell attempted to murder Harry Potter on Voldemort's orders. During a Quidditch match between Gryffindor and Slytherin, he jinxed Harry's broomstick which attempted to throw him off. Snape was aware of Quirrell's activities and muttered a counter-curse during the match to try and stop him, but Harry's friend Hermione Granger, suspecting that Snape was responsible for jinxing Harry's broom, set Snape's robes on fire. While Hermione may have got the wrong culprit, her interference had the desired effect as Quirrell's concentration was broken.
Later that year, in order to keep his master alive, Quirrell began to prey on unicorns in the Forbidden Forest and drink their blood. He met Harry, Draco Malfoy and Fang there, and was about to attack Harry when the centaur Firenze rescued the boy. About a week before Harry's exams, Voldemort ordered Quirrell to try to get the Stone again. Harry overheard this, and mistook the conversation for an argument between Snape and the Defence teacher. That night, after Dumbledore had left for London , both Quirrell and the trio went through the obstacles blocking the way to the Stone. To get past Fluffy, Quirrell disguised himself and lured Hagrid into a card game by betting a dragon's egg. During the game, he managed to draw out information about Fluffy by convincing Hagrid that he was a Dragon dealer, and as such, shared Hagrid's penchant for dangerous pets. In Hagrid's enthusiasm, and most likely under the influence of alcohol, he let slip that playing music for the three-headed dog would put him to sleep. Quirrell then sent a forged letter to Professor Dumbledore summoning him to the Ministry of Magic to get him away from the school. He went after the Stone, but was followed by Harry Potter, Ron Weasley and Hermione Granger — though they believed their enemy to be Snape.