Quirrell had joined with Voldemort and agreed to allow Voldemort's fledgling body to latch on to the back of his head. It was only able to grow into a face, and used Quirrell for transportation and sustenance.
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.
According to Voldemort, his essence could not be killed due to his creation of Horcruxes when he needed to take on a physical form, and naturally he could not return to his own body, he was able to possess living creatures and did so with animals on occasion.
At the End of the First Book. 'the servant died when I left his body and I was left as weak as ever I had been', Voldemort continued. 'I returned to my hiding place far away..." He was once again a disembodied soul, unable to use magic as he did not have any physical form, weak and helpless.
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.
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.
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.
Quirrell didn't use the Killing Curse on Harry, because Voldemort said “use the boy” to get the Sorcerer's stone from the Mirror of Erised.
Voldemort's past, as revealed by the books, is shrouded in mystery and guesswork. In fact, at the beginning of the series, barely anyone but Dumbledore and Hagrid knew that Voldemort was the charming, successful Tom Marvolo Riddle.
Bellatrix used a powerful "love potion" on Voldemort and they have sex while he is temporarily obsessed with her. She then uses obliviate on him while he sleeps (you know, he falls asleep after his post-sex cigarette) and tells everyone that the baby is her and her husband's.
Lily -Harry's mom sacrificed herself for her son leading to a spell which would not allow Voldemort to touch Harry. As Voldemort was possessing Quirell at the time, the spell started working and burned Quirell's body when he touched Harry.
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.
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.
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.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Once Hermione knew about horcruxes, she obviously looked into them. Sometime during the camping journey when she was 17 and Harry's scar hurt , the connection made sense to her. She noticed how Harry acted more like Voldemort when the locker was on, while Ron had acted insecure and her emotional.
As an unqualified wizard who didn't finish his education, Hagrid was not technically allowed to perform magic. And yet, the beloved gamekeeper seemed very magical.
Dumbledore was the first wizard to visit Voldemort, then Tom Riddle, at his Muggle orphanage. He knew even then this was a wizard to watch – and he did, closely. When Riddle applied for the Defence Against the Dark Arts post for the second time, Dumbledore turned him down.
Not knowing whether Draco was alive or dead, Narcissa chose to lie to the Dark Lord rather than risk losing her son.
Defeating The Dark Lord with his signature spell
Disarming is about defence, not murder. Voldemort was a killer, Harry was not. It was an important distinction for Harry, who had learned so much about Voldemort and seen first-hand the ways in which they were similar.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
In a way Voldemort killed himself as his own spell backfired on him. In Harry's fourth year Expelliarmus did not beat Avada Kedavra but Harry and Voldemort's wands recognized each other as twins and connected with each other in one mystical way that only a wand-maker could understand.
Later in the year, Dumbledore revealed that Harry was in fact a Horcrux, meaning that he would eventually have to die. Now, as firmly established, Snape was not the greatest fan of Harry, but that didn't mean that he ever stopped loving Lily. Dumbledore was surprised that Snape seemed to care for the boy.
Dumbledore reveals how thoroughly he loves Harry. Harry is brave, and Dumbledore is proud as any father would be. More than that, Dumbledore succumbs to a parent's weakness; he cares more about Harry's happiness and wellbeing than the wizarding world he is trying to protect.