Severus Snape

Severus Snape teaches Potions at Hogwarts in Harry Potter and the Philosopher's Stone, presiding over a cold dungeon classroom and serving as Head of Slytherin House. Sallow-skinned, with greasy black hair and a hooked nose, he opens his first lesson with a quiet speech on the subtle power of potion-making, then singles Harry out with a barrage of questions no first year could answer and takes points from Gryffindor before the hour is done. Students quickly learn that he favours his own house and that his sarcasm can find any target in the room. From that first lesson Harry is convinced the Potions master despises him, and nothing Snape does in class gives him any reason to think otherwise.