Two
Quirinus Quirell was a Muggle Studies Professor. He was a Ravenclaw, with an immense hunger of power and the unknown. Born to two pureblood parents, young Quirinus didn't know a lot about the Muggle world, but when he turned a teen he saw all the wonders Muggles had to offer.
Television, air conditioner, microwave, electricity, telephones and what not.
So he began with studying everyday Muggle life. He would note down his observations in a journal and plan to integrate Muggle technology into the wizarding world.
While doing so he also discovered the dark side of the Muggle world. He learned about guns, snipers, nuclear bombs and all types of warfare technology, which were terrible but great.
He wanted to become a Muggle Studies Professor to improve the curriculum which depicted the Muggles as if they lived in the dark ages. He wanted to warn everyone about the dangers the Muggles possess, and how it would be beneficial to take their technology and subjugate them. He wanted to present this ideas to the Dark Lord who would surely understand this.
But then came the night of 31st October, 1981.
Wherever he went, people were celebrating because Harry Potter defeated the Dark Lord. It was honestly absurd, a baby defeating the darkest Dark Lord in history? It was such a foolish concept.
So he bid his time, he knew that the Dark Lord was not gone but was waiting for his followers to come to him. But Quirell couldn't find any of his followers who were in search for him. He started to slowly gather information, out of which most were fake.
But then he was selected as the Muggle Studies Professor in Hogwarts. He was filled with joy. He did his job rater well and Muggle Studies soon became a popular subject.
He resigned in 1990 to follow the trail of the Dark Lord which was in Albania.
Spending his sweat and tears, he tirelessly searched for his Lord, scouring every inch of the the Albanian forest, when he found him.
He was reduced to nothing but a dark black cloud, but Quirell was nothing but persistent. He researched ways on how to bring him back to his former glory , where he found that there was no other way except voluntary possession. So, he let his Master and Lord to possess him.
Soon they concoted a plan to steal the Philosopher's stone which would give him a new body. But the plan wasn't without any faults, as they failed to get the stone because Dumbledore moved it.
Which brought him back to Hogwarts to teach Defence Against Dark Arts, as instructed by his Master. Dumbledore had moved the stone to the school where several traps were laid down incase anyone tried to steal it. But that wasn't the main reason he was there. His master's supposed vanquisher, Harry Potter would start his first year in Hogwarts and he would be there to ensure tha the boy savior didn't step foot in Hogwarts the next year.
The boy was sorted into Griffindor like his parents. A pity that he would have to die.
As the year progressed, Quirell slowly but steadily started solving the puzzles without trigerring any wards laid,with his Master's help. His master was mostly dormant and only came when solving the puzzles, so he was blissfully unaware about how Quirell wanted to kill the boy.
He planned to assassinate the boy on Samhain. The same day the boy 10 years ago, vanquished his master.
After the feast finished, using one of the shortcuts accessible to the teachers, he reached the 8th floor from where there would be a clear view of the entrance of the Griffindor common room. He pulled out a shrunken sniper from his pocket and enlarged it to its normal form. He then loaded the sniper with bullets and fixed it upon the spot where the boy savior was standing.
With no hesitation, he shooted the boy a headshot. And there was a pandemonium, as the children got sprayed with the boy saviour's blood. He quickly used the same shortcut to return to his chambers and hide any evidence of being the boy's murderer.
His master would be very happy.