Alan Rickman
In Harry Potter and the Philosopher's Stone (Sorcerer's Stone) Rickman portrays Severus Snape, a cold and angry professor in Hogwarts who hates Harry. This is because Severus hated James Potter, Harry's father, because James and his best friend Sirius bullied him when they were both in Hogwarts in their younger years and he sees qualities of his father in Harry. Another reason he hated Harry's father is because he loved a girl called Lily who James took and later becomes Harry's mother. However, in Deathly Hallows Part 2, it is revealed that Snape is in fact a hero. He sacrifices himself to save the wizarding world. Harry recognises this and names a child after him in honour of his bravery.