Here is the story behind Severus Snape and Hogwarts:
Snape was born in January 1960 to Eileen Prince, a pure-blood witch, and Tobias Snape, a Muggle. His childhood was not a happy one. His father was abusive, and his mother was depressed and often ill. Snape found solace in potion-making and excelled in the subject at Hogwarts.
He was sorted into Slytherin House, known for producing dark witches and wizards. Snape was not a typical Slytherin, however. He was clever, but he was also loyal and brave. He developed a close friendship with Lily Evans, a Gryffindor witch, and they fell in love.
However, Snape also joined the Death Eaters, a group of dark wizards led by Lord Voldemort. Snape was drawn to Voldemort's power and charisma, and he believed that he could use his position as a Death Eater to protect Lily.
When Voldemort learned that Lily was pregnant with Harry Potter, he made a prophecy that a child born in July would have the power to defeat him. Snape overheard this prophecy and revealed it to Voldemort, thinking he would spare Lily if he got rid of the threat to his life. However, Voldemort killed Lily and James Potter, and Snape was devastated.
Snape felt responsible for Lily's death, and he dedicated his life to protecting Harry Potter. He returned to Hogwarts as a potions professor and became Harry's mentor. Snape was often harsh and cruel to Harry, but he also secretly protected him from Voldemort and his Death Eaters.
In the final book, Harry Potter and the Deathly Hallows, we learn that Snape was a double agent all along. He had been working for Dumbledore and the Order of the Phoenix, trying to stop Voldemort from returning to power. Snape was killed by Voldemort, but he died a hero.
Snape is a complex and tragic character. He is a brilliant wizard and a loyal friend, but he is also flawed by his childhood trauma and his love for Lily. Snape's story is a reminder that even the most unlikely people can be capable of great good.