The poor boy started out life alone in an orphanage and had to deal with plenty of name calling and bullying until one day when he realized that bad things happened to people as long as he wished it hard enough. The memories following that, were filled with the young boy almost torturing his former bullies. He stole, beat and punished the other children, until he was left alone in his room at the orphanage.
His time was spent like that for years until one day he got a visitor. It was Albus Dumbledore himself! It took Quirrell a few seconds to recognize the old man, as he wasn't AS old at that point. For some reason Quirinus had thought Dumbledore always was an old man..
What struck him as odd was that he had never heard of the headmaster himself coming to tell someone of their magic and about Hogwarts. It was always the task of the professors! Quirrell would know as he had done it himself many times by now. He decided to let it slide, maybe he had a personal connection or something.
After the boy was introduced to the magical world he instantly engrossed himself into all aspects of magic and the magical world. He looked up everything from magical deities to how the government worked, so that when he joined school he would be ready to once again dominate over his peers. It didn't turn out to be as easy as he hoped.
He was at a disadvantage to begin with since he was placed in Slytherin for his ambitions, but people treated him worse than a rat in the dorms. He had to make long term plans instead of instant domination. The boy vowed to build confidence and prowess over time, so he did.
Quirinus watched as the boy learnt more and more through the years. Expanding his arsenal for every day and getting top grades in almost all subjects. He eventually proved his prowess by easily beating some upper years in duels without rules. This was when he realized his heritage. The boy always thought he was more than just a random half blood left at an orphanage and he was. He was the heir to Salazar Slytherin himself!
This shocked Quirrell to his core. Could it be? This strapping, attractive, articulate and cunning young man. Could he one day turn into the monstrous being he was in October 1981? It seemed so. After he learned of his heritage, he found the Chamber of Secrets. It was a terrible sight. He used an old demented basilisk to terrorize the school. By now he was an exemplary student with his entire house backing him. Nobody suspected him of anything.
Eventually he killed a girl by accident. Since he wasn't particularly bothered by the murder, his soul was split in half. This was exactly the result he wanted. Quirrell saw how Tom used his old diary and infused it with magic, darker than Quirrell had even heard of! He planted a part of his soul into the diary and this was apparently just the start of his plans, but it was a good start. The murder was of course not blamed on him, he managed to throw a gullible Rubeus Hagrid under the bus for it. Everyone knew he had a soft spot for dangerous creatures. Since the headmaster at the time didn't even want to have a "halfbreed" as a student, he didn't hesitate to snap his wand and throw him out. Nobody suspected a thing, except Dumbledore.
After that he laid low. Dumbledore was watching his every move ever since the whole basilisk incident, so he couldn't make his next move until after school ended. When school ended, he managed to find his real father and instantly murdered him and his entire family. He had found out what happened to all of his family and because Tom Riddle Sr. drove his mother to suicide and Tom into an orphanage, he could die for it. He went to his grandfather who also had abandoned his mother. He stole everything he had, including the Gaunt family ring, and framed him for the murder of Tom Riddle Sr.
Once that was completed, he placed a soul piece into the ring before applying for a job at Borgin and Burke's. While there, he managed to track down Hufflepuff's cup and Slytherin's locket to a lady called Hepzibah Smith. In fact he didn't have to track them down at all, after he befriended her she told him herself! So he snuck into her house and killed her with poison. He implanted a memory into her house elf to make it think it had done it accidentally, and so he put a soul piece into Hufflepuff's cup.
Soon thereafter he murdered a random muggle to put a soul piece into the locket and now his next quest was for Rowena Ravenclaw's diadem.
Throughout this time, he had been gathering followers. He had started using the name Lord Voldemort more and more, and not just with his closest circle of friends like at school. When trying to come up with ways to recruit faster he struck gold. He was going to become the Defence Against the Dark Arts professor at Hogwarts. Then he would be able to get close to any promising prospect easily and maybe tutor a few. He went in for an interview but Dumbledore rejected him.
He placed a curse on the dragon skeleton in the defence classroom as a sort of petty revenge and then walked through the halls looking for a specific someone.
He found her on the fourth floor, the ghost of Helena Ravenclaw. He convinced her (Quirrell was dumbfounded about the fact that he had even spoken to the Grey Lady but never found out who she actually was) to hand over the diadem to him so that he could once again spread the good name of Ravenclaw through the world. He always was good at persuasion but as soon as he got his hands on it, he placed another part of his soul into it and threw it into, as Quirrell now knew it was called, the room of lost things/the come and go room/the room of requirement, which Quirrell didn't know existed before he saw Tom's memories before.
Now he had five horcruxes, he was clearly aiming for six but waited with the final one. He wanted it to be special. He had even murdered a muggle to create one of them before. His last one would be spectacular.
Quirrell saw how Tom went further and further into insanity and monstrosity. He lost all humanity, not that he had much to begin with. Soon his body started slowly transforming and he lost his pretty features for more terrifying ones. His eyes turned red and then soon they reached the final memory of importance. October 31st 1981.
Quirrell had seen what was before this. He knew of the prophecy, he knew Snape was the snitch, he knew Sirius Black was innocent, but sadly he had no idea what happened at that fateful moment when he tried to murder the boy for his final horcrux. It seems not even the dark lord knows why his spell backfired.
The memories after that were fleeting, unimportant, non graphic, non sensory, not that he had felt anything in a year anyway. Finally he reached the moment when he saw himself and wondered 'Did I really look that gullible and arrogant? Is that who I am? Is that who I've always been?'
Then it struck. For the first time in ages, he felt something. Pain. Only pain. Coming from not feeling or sensing a thing for what felt like an eternity, this pain was excruciating. It came from his arm, which he was barely aware that he had anymore. Then it struck again but this time in his face. He felt something crumble and whither away. He felt himself falling down and soon with a bang, he was on the floor. Tom Riddle had left his body and the nothingness was coming for him.
Was this death? Only sleep? He had no idea whatsoever. All he felt was relief and he was grateful towards the boy who caused this. He knew what had happened, his skin burned off as soon as the boy touched him. He didn't know why but that was certainly what happened. Now his eyes were closing, he felt his eyes! A second later and it was all gone. All black. All empty. He knew no more, and then he woke up.
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A/N: Btw the thing about him thinking it was strange that Albus came to visit Tom wasn't actually strange. He just assumed at first that Albus was Headmaster at that time since he didn't know it was THAT long ago. Albus was a transfiguration teacher at the time btw if you didn't know. Probs deputy headmaster and head of Gryffindor as well but I don't know that
Also that's the end of the prologue, now he will actually interact with the world again.