At times, Snape could appear cold, cynical, malicious, bitter, and sarcastic. He had a commanding presence that exuded gravitas, authority and control; like Professor McGonagall, he had the ability to keep a class quiet without effort. He tended to hold grudges and was extremely spiteful toward those whom he disliked. In particular, he disdained Gryffindor students, considering them to be arrogant and attention-seeking. Descriptions of his social interactions as a child suggest that he had poor interpersonal skills.
Snape was a repressed, solitary man with no friends. In his early life, he was insecure, vulnerable, and yearned to be part of something better. As a child, the bleak normality of working-class suburbia compounded with his neglectful Muggle father inspired in him a contempt for ordinariness. This urgent desire to be a part of something powerful and important was what drew him to Lord Voldemort's inner circle. Snape's bitterness and resentment towards the world was exacerbated even more by the relentless bullying he endured in school, causing him to shut himself in even more. Snape was not a prejudiced individual despite the Death Eater beliefs of pure-blood superiority, but was rather against towards Muggles, presumably because of his sour experience with both his father and Petunia Evans, but held no ill-will towards Muggle-borns. The foundation of him scolding Lily Evans by calling her Mudblood was to not appear weak in front of his fellow Death Eater students than actual supremacist views. He also deeply regretted this as it was what ended his friendship with Lily and defended Hermione Granger when Phineas Nigellus Black called her Mudblood, his manner of speaking in this instance being uncharacteristically explosive and filled with more emotion than he normally displayed.
He was an intensely private individual who viewed emotional displays as a sign of shameful weakness. As an Occlumens, Snape had superb emotional control and was adept at concealing his thoughts and feelings, which allowed him to maintain his cold, collected demeanour. However, he had his limits, and was not incapable of losing his temper, particularly when it came to dealing with Harry Potter. Inevitably, he also became furious when he thought he was being pitied or accused of cowardice.
Snape was a formidable sorcerer, displaying consummate skill in many different branches of magic. His extensive knowledge and abilities were rivalled by very few, if any other witches and wizards of his age. Snape was also unusually cerebral for a wizard, possessing a subtle and keenly analytical mind. As a result, Snape was extremely intelligent and calculative, with a mind for strategy and deduction. He was also a profound misanthrope who appeared to have a prominent hatred of almost every child under his tutelage, except of course for Slytherins. He valued logic and cunning above magical power.
As a professor, Snape was known for his cavalier and harshly authoritarian attitude towards his teaching. His standards for his classes were much higher than that of the other professors, as he only allowed students with the very best grades to continue into advanced study. He developed a loving passion for Dark Arts, originally in the hopes to cover the shame of his heritage, and his interest in it led him to repeatedly apply for the Defence Against the Dark Arts professor post every year, despite being rejected for sixteen years. When he finally got his wish, Snape taught the course with a loving caress in his voice, far beyond simply respecting the Dark Arts as a dangerous foe, something he did not show in his post as the Potions Master. He also taught this class slightly fairer than he did in Potions, such as lowering his entrance standards and biassed for the N.E.W.T. level, allowing more students to enter the advanced studies of his favourite class, and placed students from his own house, such as Vincent Crabbe and Gregory Goyle, in detention for failing to do acceptable work the second time around after failing their O.W.L. the previous year.
Ultimately, it was Snape's past and his love for Lily Evans that defined his inner being. His love for Lily Evans became most noticeable by his patronus, a Doe, just like Lily's. Upon overhearing the Prophecy, he immediately informed his then-master of its contents, unaware that this would endanger Lily and her family. It was only after Lily's death that Snape realised the full extent of his actions. He suffered terrible remorse for what he had done and spent the rest of his life in constant danger in order to protect Lily's son. "You are a braver man by far than Igor Karkaroff. You know, I sometimes think we Sort too soon..." —Albus Dumbledore after Snape informs him that Karkaroff is planning to flee once Lord Voldemort returns[src] In spite of his vindictive demeanour, Severus Snape was an immensely brave man who possessed a deep capacity for love. Everything that he did in the latter part of his life was motivated by his devotion to Lily Evans, whom he loved unconditionally. He was one of Dumbledore's most reliable allies and in his role as a double agent, took great personal risk in ensuring Harry's safety from Lord Voldemort. Despite his years of him and Harry barely getting along, if at all, Snape openly criticised Dumbledore after learning he protected Harry all these years just so he could die at the right time due to being a Horcrux, showing he's grown to genuinely care for Harry, even though at first, he only protected him because of his relationship to Lily. When he informed Dumbledore that he informed Voldemort of the prophecy, Snape begged Dumbledore to hide Harry, Lily, and even James too. This clearly showed Snape prioritised Lily's happiness above all else, even if it meant her being with a man he hated for most of his life.
Despite Snape's normally calm and controlled exterior and guarded body language, he was in possession of an extraordinarily explosive and almost psychotic temper. This was rarely seen, but extreme display of rage was most prominently witnessed after Snape killed Dumbledore and was confronted outside of Hagrid's burning house near the edge of the school grounds. The event that triggered this unhinged manifestation of Snape's unrestrained wrath was Harry's accusation of Snape being a coward for killing Dumbledore. Due to the many years of being bullied by Harry's father, and with a need to both vent his immense stress and maintain his cover, Snape unleashed a terrifying mix of both his emotions and magic, taking great pleasure in torturing and punishing the son of his enemy. Unlike in the past where he spoke quietly in his anger, Snape in this instance was screaming and letting so much out, and confessing his identity of the Half-Blood Prince to Harry who had attempted to use one of Snape's own invented spells against him. This battle showed Snape's repressed rage in its horrific glory and power. Suffice it to say, Severus Snape was not a man who it was wise to provoke, lest one incur his almost elemental wrath and magical power.
Severus Snape was a slender, thin man with sallow fair skin, a large, hooked nose and yellow, uneven teeth. He usually dressed in flowing black robes which made him resemble "an overgrown bat". He had shoulder-length, greasy black hair, curling lips and brown eyes. As a Death Eater, he bears the Dark Mark on his left inner forearm.
He always dons a black button shirt, with matching trousers, shoes and a floor length cloak. He carries his own wand.