Sometimes, in films, roles are recast because the original actor cannot find time to reprise their role, or sometimes, due to natural causes. For example, the role of Albus Dumbledore was portrayed by Michael Gambon from the third-eighth film due to former actor, RIchard Harris's death.
However, it turns out that more characters in Harry Potter have been recast. So, here are the top 5 most interesting ones:
1. Cedric Diggory
You have to know Cedric Diggory as being portrayed by Robert Pattinson in Goblet of Fire. And some of you more uncultured folk know a sparkly vampire as being portrayed by Robert Pattinson. However, it turns out that Cedric, in canon, would have been the seeker in the Quidditch game in Prisoner of Azkaban.
However, the thing is, no one even KNOWS who portrayed Cedric in Prisoner of Azkaban. I'm pretty sure now, he's just selling sandwiches at his local Arby's wondering how he went wrong.
2. Hermione's Parents
You might think that the only appearance that Hermione's parents had was at the beginning of Deathly Hallows Part I portrayed by Michelle Fairley and Ian Kelly. However, it turns out that they made an appearance in Chamber of Secrets, portrayed by Heather Bleasdale and Tom Knight.
3. Tom the Bartender
In Sorcerer's Stone, the role of Tom, the bartender in The Leaky Cauldron, is portrayed by Derek Deadman. However, in Prisoner of Azkaban, the role is portrayed by Jim Tavare.
HOLY SHOOT!!! What crack was he on?! What happened to him? He's supposed to look like a British guy, not freakin' Mr. Clean.
4. The Fat Lady
In Sorcerer's Stone, the Fat Lady was portrayed by Elizabeth Spriggs. However, in Prisoner of Azkaban, when the Fat Lady was given a much more humorous role, she was portrayed by Dawn French. Her role in the third film included her singing, which was not used in the book.
5. Helena Ravenclaw
Helena Ravenclaw had made a small appearance in Sorcerer's Stone, when Nearly Headless Nick is telling her about how Harry was the new Seeker.
She was then portrayed by Nina Young. However, in the final film, when she had a larger role, she was portrayed by Kelly MacDonald.
And that's it!