Three years ago, Alan Rickman sadly passed away at the age of 69 following a battle with pancreatic cancer. The actor was best known for his roles as Hans Gruber in Die Hard, the Sheriff of Nottingham in Robin Hood: Prince of Thieves and, of course, Professor Severus Snape in the eight Harry Potter movies. ("Five points from Gryffindor!")

It's hard to imagine anyone else playing Snape, the sarcastic sourpuss who appears to serve the Lord Voldemort, but is actually a double agent working for Albus Dumbledore and The Order Of The Phoenix. Through the course of the movies (and books), we learn his true motives, and his tragic backstory, harboring unrequited love for Harry Potter's mother, Lily.

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When Rickman agreed to take the part, only three Harry Potter books had been published. At first, the actor was skeptical, wondering if 'Professor Snape' was just a one dimensional character. However, author J.K. Rowling had the story mapped out, and changed Rickman's mind by sharing a secret piece of information: what lies behind the word "always." (Snape's Patronus takes the shape of Lily Potter, his long-lost love.) Far from being a caricature, Snape's heartbreaking story arc is arguably the best in the saga.

In 2011, Rickman wrote an emotional letter to the Harry Potter films after wrapping the final installment, Harry Potter and the Deathly Hallows: Part 2. Here's the full text, courtesy of Empire Magazine:

"I have just returned from the dubbing studio where I spoke into a microphone as Severus Snape for absolutely the last time. On the screen were some flashback shots of Daniel, Emma, and Rupert from ten years ago. They were 12. I have also recently returned from New York, and while I was there, I saw Daniel singing and dancing (brilliantly) on Broadway. A lifetime seems to have passed in minutes.

"Three children have become adults since a phone call with Jo Rowling, containing one small clue, persuaded me that there was more to Snape than an unchanging costume, and that even though only three of the books were out at that time, she held the entire massive but delicate narrative in the surest of hands. It is an ancient need to be told in stories. But the story needs a great storyteller. Thanks for all of it, Jo."

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On Twitter, Harry Potter fans are raising their wands for Alan Rickman, who brought one of the most memorable characters in fantasy to life. While he was taken from this world too soon, his work in film and television lives on.

Maybe Rupert Grint, who played Harry Potter's sidekick, Ron Weasley, said it best, "I am devastated to hear about the passing of Alan Rickman... Even though he has gone, I will always hear his voice." Indeed, you can never forget how Rickman sneered, "Potter!" That was pretty good, Ron. Five points to Gryffindor!

This is the emotional letter Alan Rickman wrote to the 'Harry Potter' films just after they finished filming