As of 2009, Severus Snape has appeared in all six Harry Potter films, portrayed by British actor . Rickman was Rowling's personal choice to portray the character. He had conversations with Rowling about his character and is one of the few Harry Potter actors that she spoke to prior to the completion of the book series about the future direction of the character. "He knew very early on that he'd been in love with Lily," said Rowling. "He needed to understand […] where this bitterness towards this boy who's the living example of her preference for another man came from."
Snape's true loyalty was one of the most significant questions in the series up until the end of the final instalment, . Although the first five novels depict him as unfair and vindictive towards Harry and his friends, he invariably ends up protecting or otherwise helping them when they or their allies are in danger. Several characters express doubts about his loyalty, but Dumbledore's trust in him is generally taken as the final word. The sixth novel, , departs from that model. In the second chapter, Snape claims to have been working for Voldemort ever since the latter's return, and only pretending to help Dumbledore. By killing Dumbledore toward the end of the novel, Snape seems to place himself firmly in Voldemort's camp. Rowling maintains this impression through the early chapters of the seventh novel. However, near the climax of the book, Snape leaves Harry his dying thoughts (to be viewed in the Pensieve) and ultimately reveals to Harry that he had been loyal to Albus Dumbledore throughout the series. Snape's loyalty to Dumbledore stems from his fierce devotion to and love of his childhood friend, , Harry's mother.
After the completion of the series Rowling began to speak openly about Snape and admitted that she was particularly pleased with the way Snape's story played out throughout the course of the series, contrasting his with that of . Rowling said, "the series is built around [Dumbledore and Snape]", and maintained that she always knew what Snape would turn out to be at the end and that she carefully plotted his storyline throughout the series. "I had to drop clues all the way through because as you know in the seventh book when you have the revelation scene where everything shifts and you realize why Snape was…what Snape's motivation was. I had to plot that through the books because at the point where you see what was really going on, it would have been an absolute cheat on the reader at that point just to show a bunch of stuff you've never seen before." Rowling further said in an interview that she wanted Snape to find redemption and forgiveness: "Snape is a complicated man... he's a very — he was a flawed human being, like all of us. forgives him — as we know, from the epilogue, Harry — Harry really sees the good in Snape ultimately... there's redemption."