From Harry’s very first Potions class, Severus Snape has given Harry a hard time, and that is perhaps putting it mildly. Snape is Head of Slytherin House and teaches Potions at Hogwarts. In book five, we find out that he has been teaching at Hogwarts for fourteen years and that it is true he has tried to apply for the Defense Against the Dark Arts position every year only to be rejected by Dumbledore. Snape is probably the most interesting professor at Hogwarts, mostly because of his dark and mysterious past. Throughout the books, we slowly find out more about him.
Snape went to Hogwarts at the same time as the Marauders (about twenty years ago), but they were adversaries. Snape and Sirius Black especially hated each other, and Sirius played a trick on Snape that involved Snape almost getting killed by Lupin in his werewolf form. James Potter saved Snape’s life, but for some reason (probably because he hates to owe anybody), Snape really hates James Potter as well, and for this reason, he holds his grudge against James’ son Harry. Also, Snape was a Death Eater at one time, but for some unknown reason, he turned himself in to Dumbledore, and as penance for his sins, he has been working as a spy for Dumbledore. Dumdledore is probably the only person Snape really respects and feels any sort of gratitude toward.
He is extremely strict in the classroom and won’t hesitate for a moment to remove points from Gryffindor, especially if Harry is involved. Often coming across as heartless and cruel, Harry has grown to despise Snape even more by the end of his fifth year. Despite the fact that Snape saved Harry’s life during his first year (the enchanted broom incident during Quidditch) and fifth year (by alerting the Order that Harry and his friends had gone to the Ministry to save Sirius from Voldemort – or so they thought they were doing so), Harry has displaced his hatred on to Snape (probably because he knows that Snape taunted Sirius about not being able to do anything useful for the Order). Chances are that Snape is concerned for Harry more than Harry may ever realize it, but his methods are harsh, and he doesn’t tolerate weakness, which is made quite clear during Occlumency lessons.
There is no doubt that there is still much to be discovered about Snape. His character is so complex and ambitious, but utterly intriguing, that it’s hard to say for sure what he may do in the sixth and seventh books. Recognition and pride are very important to Snape, and he would more than likely do anything within his power to achieve his ambitions.
Snape is highly intelligent and cunning. He is bitter, sarcastic, and probably what could be considered a broken man. According to JKR, he is about 35-36 years old during Harry’s fourth year. He has greasy black hair that hangs to his shoulders, black eyes like tunnels, a large hooked nose, thin lips, pale skin, and is tall and thin. He is yet another character described as having long fingers. Snape always dresses completely in black and lives in the dungeons of the school. His robes have been described as billowing, and the way in which he moves around is bat-like. His voice is low, smooth, and dangerously silky when he is quite angry.