Professor Severus Snape was a half-blood wizard and son of Tobias and Eileen Snape . During his lifetime, Snape was Potions Master , Defence Against the Dark Arts professor , and Headmaster of Hogwarts School of Witchcraft and Wizardry . He was also a member of the Order of the Phoenix and played a very important role in both of the Wizarding Wars against Voldemort.

Snape was raised in the Muggle dwelling of Spinner's End, which was in close proximity to the home of the Evans family, though in a poorer area. He met Lily and Petunia Evans when he was nine, and fell deeply in love with Lily, becoming a close friend of hers. In 1971 he began his first term at Hogwarts where he was Sorted into Slytherin House. This put him in the same year as Lily but unfortunately for him, in rival houses. Severus became the immediate enemy of James Potter and Sirius Black and was a frequent victim of their bullying. Snape developed a passion for the Dark Arts at a young age, which increased as his desire for revenge grew stronger. Snape became involved with the bullies in Slytherin House, many who were pure-blood supremacists. This put his friendship with Lily, a Muggle-born, under great strain, until it was eventually broken in their fifth year. In an attempt to win back Lily's affections, Snape joined the Death Eaters along with a group of his fellow Slytherins.

Severus was made a member of the Slug Club, presumably because of his brilliance at potion-making, and Horace Slughorn kept a picture of him as a student, clutching his copy of Advanced Potion-Making. Despite this, Horace did not have many hopes for Severus's future, as his photograph was kept behind many others.

Shortly before Lily Evans was murdered by Lord Voldemort, Snape changed sides and became a member of the Order of the Phoenix and double agent during the Second Wizarding War. With tremendous difficulty, Snape prevented Lord Voldemort from learning the truth about his loyalties. Despite the opinions of most others including Harry during his early life, Albus Dumbledore trusted Snape for reasons that were kept between them both until their deaths. When he died, it was revealed that his deep strong love for Lily Evans caused him to redeem himself, joining Dumbledore's cause at the prospect of her protection (and, after her death, that of her son) from Lord Voldemort.

The relationship between Dumbledore and Snape would be one of an unusually strong loyalty, so much so that Snape agreed to kill Dumbledore upon Dumbledore's own request. Before Dumbledore's death, Snape promised to protect the students of Hogwarts from the Death Eaters, who would inevitably take control of the Ministry of Magic, as well as the school. Snape later participated in the Battle of Hogwarts, but was murdered by Lord Voldemort who mistakenly believed that Snape was the master of the Elder Wand (an immensely strong and powerful wand that Voldemort deeply desired, one of the Deathly Hallows) when in reality, Harry Potter was the master of the Elder Wand, because Draco Malfoy had disarmed Dumbledore, on the night of Dumbledore's death on top of the Astromony Tower and Harry had disarmed Draco at Malfoy Manor.

After his death, Harry Potter ensured that Severus Snape's portrait remained at Hogwarts, honouring him as a hero, despite their significant personal differences. In addition Harry later named his second son Albus Severus Potter in honour of Dumbledore and Severus, both an inspiration in Harry's life after the Battle of Hogwarts. Harry also was influenced by Severus's Hogwarts house, and freely admitted that Albus could choose Slytherin if he wished.