However, Voldemort, after finding out that he taught at Hogwarts, took over his body, subsequently turning him into a temporary Horcrux, though Quirrell put up some feeble resistance. He died in vain while trying to murder Harry Potter in the Underground Chambers.
When Quirrell came across him in the forest, Voldemort was able to possess him the same way he had been possessing animals, as he was at that point pure spirit and had no body of his own to inhabit. Using magic, presumably.
Quirrell tried to put up feeble resistance on occasion, but Voldemort was far too strong for him. Quirrell is, in effect, turned into a temporary Horcrux by Voldemort. He is greatly depleted by the physical strain of fighting the far stronger, evil soul inside him.
Quirrell is considered a horcrux. However, the reason it is not always mentioned is because he was a temporary one and as the first one to be destroyed, the connection is never made in the books, but by definition Quirrell is in fact a horcrux. "Quirrell is, in effect, turned into a temporary Horcrux by Voldemort."
As for how Voldemort got onto Quirrells head, it is unclear, but some think it might be because Quirrell had made a blood pact with him when they both were working at Hogwarts. Quirrell was unable to resist Voldemort's will and was forced to do his evil deeds.
Quirrell is defeated by Harry upon physical touch, which burns him and allows Harry to break the chokehold. Harry cuts off his access to the stone and touches him, forcing him back, and he disintegrates, crumbling to ash and dust at Harry's feet, dead, and becoming Harry's first kill and victory.
It should be noted that despite his fear of Voldemort and that he was not a Death Eater, Quirrell was one of Voldemort's only followers who referred to him by name, the others being Barty Crouch Jr. and Peter Pettigrew.
Originally Answered: Did Snape know that Quirrell was hosting Voldemort? No. Snape did not know Quirrell was hosting Lord Voldemort during the events of Book 1. He tried to stop Quirrell from acquiring the Sorcerer's Stone on Dumbledore's orders.
Albus Dumbledore: I had my suspicions about Professor Quirrell, but I saw no concrete evidence of wrongdoing. I felt it was more important to give him the benefit of the doubt and keep a close eye on him, rather than dismiss him without proper cause.
Lily's sacrifice and her love saved Harry. Voldemort can not comprehend love, and so it destroys him to touch Harry because Lily's love for her son runs through Harry's veins and body. ems Harry burnt Quirrell's face when he touched it.
The most likely reason why Lord Voldemort's nose disappeared and he devolved into such an evil-looking creature is that as he dabbled deeper into the Dark Arts, his appearance gradually became as distorted as what remained of his twisted soul.
There is also a strange smell of garlic that hangs about the classroom; the Weasley twins insist that it is because Quirrell has stuffed his turban full of garlic to ward off vampires.
Voldemort wasn't aware of Harry being a pseudo-horcrux because he didn't plan it, and Harry didn't know either until Voldemort “killed” him, but he actually killed the piece of soul kept in him.
When Quirrell takes a trip to Albania, the last rumored location of Voldemort, and comes back a stuttering mess, Dumbledore probably instantly knew what was up. He just couldn't catch him in the act. So, he let him go for the Stone.
The Horcruxes Left Him Vulnerable & Weak
Although they did give Voldemort another chance to join the living after his curse against Harry Potter rebounded, they harmed him in the long run. In creating these Horcruxes, he gave the ability for other witches and wizards to destroy him without ever laying a finger on him.
Pettigrew mixed up a potion for Voldemort using unicorn blood and the venom of Nagini. With this potion, they were able to create a new body for Lord Voldemort to finally return to. However, this body was not what Voldemort needed to return to his fearful leadership form. Instead, it was that of a scaly, hairless baby.
Snape did not need to tell Dumbledore about Quirell because he already knew. It was Dumbledore who told Snape to keep an eye on Quirell because the former already had his suspicions. Snape was not able to accumulate solid proof but otherwise Dumbledore was well in the loop.
Voldemort's desire to beat death and become immortal was also why he and Quirrell ended up slaying innocent unicorns. Drinking the blood of a unicorn would keep someone alive – even if they were an inch from death.
Voldemort was almost in control of Quirrell's body by that time. Voldemort controlled Quirrell as to attack Harry. This activated Lily Potter's magic where Voldemort is not even allowed to touch Harry. And that's why Harry was able to burn Quirrell down.
Snape's fierce devotion to and love of his childhood friend Lily, Harry's mother, is the foundation of that loyalty. After Harry Potter and the Half-Blood Prince, Snape's loyalty was a matter of intense debate among the fans.
"Hagrid is one of Voldemort's oldest associates, and knows his true identity" In Chamber of Secrets, it is revealed that Hagrid had been a student at Hogwarts during the same period that Tom Riddle (the true identity of Lord Voldemort) also frequented the school.
Quirrell knew he wanted a dragon egg and used it to manipulate Hagrid into telling him how to get around Fluffy. Hagrid then went to the Library to borrow books on caring for a dragon. Harry Potter, Ron Weasley and Hermione Granger found the section he was browsing and deduced why.
Peter Pettigrew (a.k.a. Wormtail) is the only Death Eater known to have been in a House other than Slytherin (Gryffindor) while at Hogwarts. There, he was a close friend of Sirius Black, James Potter, and Remus Lupin, although he was the least intelligent and least talented of the group.
Having gone through the horrors of the second wizarding war as a Death Eater, Draco abandoned the pure-blood beliefs he was originally devoted to, and grew to become a better person than he was in his youth, growing more tolerant and accepting of the non-pure-bloods of the wizarding world.
Professor Quirrell
"Master, I cannot hold him — my hands, my hands!" No one was very sad about the literally two-faced Quirrell's death.