Alan Rickman was one of the few actors in the Harry Potter franchise that J.K. Rowling actually disclosed information about his character before the storylines had been written.
Rowling didn’t disclose everything she had in mind for Snape to Rickman, but she did tell him “what lies behind the word ‘always’” – the character’s famed line in the franchise.
Rickman had often been typecast as the villain and he was growing weary of it.