Severus Snape grew up in Spinner's End with only a fellow young witch - Lily Evans - as a friend for his earliest years. Even after their friendship frayed during their time in Hogwarts together, Snape's love for her never faded, and he did everything to try and win her back - even joining the Death Eaters. When it was clear he had been betrayed when Lord Voldemort killed Lily, Snape's loyalty returned to Dumbledore and his army, with the help of Albus Dumbledore's support to clear his name. Snape remained loyal to Dumbledore until the very end, even if he appeared as the villain to the masses, as his position put him at an advantage for working undercover during Lord Voldemort rising back to power.
Snape was killed by Lord Voldemort's snake in the Shrieking Shack on 2nd May 1998. Before he passed away, he extracted his memories so the truth of his life could be revealed to Harry Potter.

Severus Snape was born on 9th January 1960. He was the only child of Tobias Snape (muggle) and Eileen Prince (pure-blood), born and raised in Spinner's End, England. His parents fought constantly, and it wasn't the happiest of upbringings. It was during this time that he first met a witch around his age. Young Lily Evans, who quickly became his friend, and first love, at only the age of 9.

Severus Snape started Hogwarts in 1971 and graduated in 1978. He journeyed to the school the same year as his friend, Lily Evans. He shared a compartment on the Hogwart's Express with her, along with James Potter and Sirius Black. Severus instantly took a disliking to the two boys. During the sorting, he was placed into Slytherin, and Lily ended up in Gryffindor with James and Sirius. Although their friendship did not end instantly, their divide was the start of the end. Over the years, Severus ended up getting caught up with a group of Slytherins who all shared similar views towards muggle-borns - bullying them and believing they don't belong in the school. Even still, Severus didn't have it easy, as he constantly clashed with James and his friends and them trying to humiliate him. It was one instance during his 5th year when James cast a spell to not only suspend Severus upsidedown but also to reveal his underwear. At witnessing Lily seeing him in that state, he lashed out at her and called her a "Mudblood", which was something he regretted and tried to apologise for. Lily never forgave him, and the two went their separate ways.

Severus was an exceptionally talented wizard during his time at Hogwarts, with enough talent to invent several spells. As well as the spells, Severus had a keen interest in potions and had enough skill to scribble his own notes down for alterations to existing recipes under the alias of 'The Half-Blood Prince'. This notebook would likely remain in the school, as it later falls into the possession of Harry Potter in 1996.

After graduating Hogwarts, Severus, along with the majority of his misguided Slytherin gang, joined the ranks of the Death Eaters in support of Lord Voldemort. Severus' role in the First War was rather unknown until 1980, when he overheard a conversation between seer and Divination Professor - Sybill Trelawney - and Albus Dumbledore, involving a prophecy telling of Lord Voldemort's ending. After relaying this to Lord Voldemort himself, Snape became one of the most trusted people at the Dark Lord's side.

After Severus learnt that the Prophecy involved Lily Potter (Née Evans), he tried to stop Voldemort from acting. Eventually, he resorted to Albus Dumbledore for help in a bid to try and keep Lily safe. Although the plan failed, Snape remained loyal to Albus Dumbledore from that moment on and vowed to keep Lily and James' only son, Harry Potter, safe. The curse the Dark Lord cast to try and kill Harry the night of Lily and James' death rebounded, and Voldemort disappeared that night.

Severus began teaching at Hogwarts in 1981 as the new Potions Master. He didn't care much for Harry Potter joining the school in 1991, but he still did his best to stop any real harm from coming to him - saving the boy's life on more than one occasion through the years (even if Harry wasn't fully aware of it at the time).
When Lord Voldemort returned in 1994-1995, Severus joined Dumbledore's allies for fighting back against the dark forces, 'The Order of the Phoenix'. However, Harry Potter doubted him multiple times, believing him to be a traitor to the cause. Little did Harry Potter know at the time that Severus was playing the role of a double agent. He returned to the side of the Dark Lord and was quickly back to being a trusted ally by him, even if some of the Death Eaters doubted his loyalty. In 1996-1997, Severus became responsible for Draco Malfoy - Harry Potter's nemesis at the time. The Malfoys were loyal servants to the Dark Lord, but Draco's mother asked Severus to take an Unbreakable Vow to keep her son safe, as Lord Voldemort assigned him a mission to prepare the young boy for becoming a Death Eater just like his father.
Severus Snape carried out the wishes of Albus Dumbledore, along with keeping the Unbreakable Vow to Narcissa Malfoy, and he murdered Albus Dumbledore with a killing curse in place of Draco Malfoy. Although deemed a traitor by all he had worked with in the Order, Severus did what he could to still try and protect as many as he could from the dark forces. Unknown to Harry Potter, Severus guided the boy (with his patronus) to the sword of Gryffindor, which he could then use to destroy one of the Horcruxes to weaken Lord Voldemort. Severus even became Headmaster of Hogwarts in 1997 in a bid to protect the students from the Death Eaters, all while still being trusted by the Dark Lord.
Severus Snape was bitten by Nagini, Lord Voldemort's snake, and eventually succumbed to the poison. He died in the Shrieking Shack during the Battle of Hogwarts, 2nd May 1998. He did not die due to Lord Voldemort doubting his loyalty but simply because Lord Voldemort believed him to be the true owner of the Elder Wand, which he was trying to master. Severus remained conscious long enough to extract his memories to reveal the truth of his loyalty and double life to Harry Potter. He lived his life as a traitor to the public eye and was only hailed a hero in death.