Name: Severus Snape
Fandom: Harry Potter
Age/Point in canon: 38 (appears 17) / Trio-Era
Boggart: Lily Evans, dead
Titles: Potions Master, Potions Professor, Head of House, Headmaster
Severus Snape grew up in the Muggle village known as Spinners End to a Muggle father named Tobias Snape, and a potion prodigy wizard named Eileen Prince. He had little money growing up, thus lived without many things that other children had, developing a bitterness for people who took what they had for granted.
His magical prowess was not hidden from him, and he knew that he would eventually attend Hogwarts School of Witchcraft and Wizardry. He wished to be a Slytherin, because he felt that it was an excellent combination of the strengths of the rest of the houses. In a search for others like him, he discovered Lily Evans, a Muggle girl who was displaying magical abilities. Despite an unfortunate first impression, the two developed a strong friendship that lasted over the majority of their school years, even going so far as to surpass the animosities that existed between their houses and circle of friends... for a time. Severus developed strong romantic feelings for Lily, which were never returned, and she instead fell in love with Severus's long-time rival, James Potter. Severus's bitterness grew.
He fell in league with the wrong crowd - the Death Eaters - proving his worth through his potion skill and inherent understanding of the Dark Arts (a side effect of the constant teasing he suffered growing up). He was a loyal servant to the Dark Lord - arguably, one of his strongest followers - until the year of the prophecy. Lord Voldemort discovered that the one who would defeat him would be born, and made the decision that it was Harry Potter. Though Severus begged him to spare the mother, Voldemort's compassion was non-existent, and Lily Evans/Potter was killed.
But though the world ended for Snape that day, all was not lost.
In desperation, knowing that his unrequited love was close to death, Snape had turned to the only man that he believed could stop Lord Voldemort's destruction - Albus Dumbledore. He begged Dumbledore to do everything he could to protect Lily and her family, not caring what cost he would have to pay to ensure her safety. Though Dumbledore was unsuccessful in his promise to protect the Potters, one survived. One scrap of Lily Evans remained in the world - her son. Under Dumbledore's suggestion, and guidance, Severus Snape pledged what was left of his shambled life to protecting the one part of his love that had survived the war - and asked that his secret not be revealed. Until the moment he died, Severus Snape appeared to be a double-crossing murder. Though seen from different eyes, he was the strongest of them all.