When movies are adapted from beloved books or comics, the casting process can get a bit hairy. Everyone has their own idea of what their hero or heroine should look like on the big screen, and many times a filmmaker has got it really wrong – Tom Cruise as 6ft 5in tough guy Jack Reacher, for example? Or Ryan Reynolds as Green Lantern?

Sometimes, even though fans may be outraged or it looks a bad idea on paper, a controversial casting decision can turn out to be the right one all along. Here are nine casting risks that shouldn't have worked... but did.

1. Heath Ledger – The Joker (The Dark Knight)

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Batman fans are very hard to please. They weren't enthusiastic about Michael Keaton (see below) or Ben Affleck being cast as Batman, and they also got their capes in a twist over the casting of Heath Ledger as The Joker in Christopher Nolan's The Dark Knight.

DC Comics fans took to the internet to complain, angrily writing "I am NOT seeing this movie if he is in it," "some pretty boy as The Joker? No!" and "The Joker is a character that needs an actor with gravity. Not some little twerp who got lucky" (Ouch).

Seems they all preferred Paul Bettany, who was tipped for the part, rather than the star of 10 Things I Hate About You and Brokeback Mountain.

To be fair, who predicted the diabolical, mesmerising Joker who appeared onscreen in 2008? Ledger's performance eclipsed Christian Bale's Batman in every scene, but he never got to hear the critical praise – or see the Batfans eating their words – as he died six months before the film was released.

In February 2009, Heath Ledger was posthumously awarded a supporting actor Academy Award for his searing performance.

2. Gal Gadot – Wonder Woman (Batman v Superman: Dawn of Justice)

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A live action Wonder Woman has been in the works in Hollywood for almost two decades, with Sandra Bullock, Catherine Zeta Jones, Angelina Jolie, Beyoncé and even Mariah Carey considered for the role of the other Princess Diana.

In 2013, director Zack Snyder cast Gal Gadot in the role for Batman v Superman: Dawn of Justice, and the Israeli actress instantly had to defend her casting when DC fans complained she was too skinny, and wasn't as busty as TV Wonder Woman Lynda Carter. Gadot's response was perfect: "She is Amazonian, and historically accurate Amazonian women actually had only one breast!"

In the end, Gadot's cameo performance was hailed as one of the best parts of Batman v Superman, and this year's Wonder Woman movie turned out to be one of the biggest box office hits of the summer (a sequel follows in 2019, and Wonder Woman will also make an appearance in Justice League this November).

3. Michael Keaton – Batman/Bruce Wayne (Batman)

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We'll come right out and say it – Michael Keaton is the best movie Batman (sorry, Christian Bale, but you were just too sulky).

However, when he was cast in Tim Burton's 1989 movie, fans of the character weren't at all keen. At the time, Keaton was best known for comedic roles in movies like Mr Mom and Night Shift, and more than 50,000 letters of protest about his casting were sent to Warner Bros. Even Burton himself hadn't always wanted his Beetlejuice lead for the role – he had approached both Pierce Brosnan and Ray Liotta before settling on Keaton.

The worry was that it would end up being camp like the '60s TV series, but the end result was a darker Batman than had been seen before, with Keaton terrific as the billionaire with a secret love of bats.

And while the movie wasn't perfect – Jack Nicholson's Joker swallows up the screen, and Prince's soundtrack also dominates – Keaton returned to the role for what remains one of the best Batman movies, 1992's Batman Returns.

4. Renée Zellweger – Bridget Jones (Bridget Jones's Diary)

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Bridget Jones is, of course, the pudgy, English thirtysomething subject of Helen Fielding's bestselling comic novels.

Helena Bonham Carter, Emily Watson, Rachel Weisz and Toni Collette were reportedly all considered for the role in the 2001 movie based on the book, but after a two-year search it was glamorous American actress Renée Zellweger who won the part.

Fans of the very British heroine grumbled loudly about her casting (she's too thin! she's from Texas!), leading co-star Hugh Grant to gallantly leap to her defence in Entertainment Weekly during filming. "She is bang-on, she's very funny and she's been living in England a long time now, mastering the accent. It'll be a triumph. I know it will."

Of course, he was right. Zellweger gained 20 pounds for the role, worked with an accent coach (Barbara Berkery, who also coached Gwyneth Paltrow for Shakespeare in Love) and when the movie came out was nominated for an Oscar and a BAFTA for her terrific performance.

5. Daniel Craig – James Bond (Casino Royale)

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When Layer Cake actor Daniel Craig was announced as the successor to suave Pierce Brosnan in 2005, James Bond fans were not happy. Before the film was even finished, die-hards were encouraging moviegoers to boycott Casino Royale, and a dedicated website (craignotbond.com) emerged to claim, "Eon cast a short, blond, odd-looking Daniel Craig in the role of Bond. Craig, described by the New York Times as having a 'pale, flattened face and large, fleshy ears' is a terrible choice!"

Four previous Bonds – Brosnan, Sean Connery, Timothy Dalton and Roger Moore – all defended Craig's casting and, of course, the box office proved Eon Productions knew what they were doing.

Casino Royale made nearly $600 million worldwide, becoming the top-grossing Bond movie at that time. Craig's grittier, cooler Bond has become a fan favourite and Craig's third outing as 007, 2012's Skyfall, is now the most successful Bond movie ever.

Last month, Craig confirmed he is returning for a fifth and final Bond movie, due for release in November 2019.

6. Tom Cruise – Lestat (Interview with the Vampire)

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A contentious one this, as fans of Anne Rice's Vampire Chronicles novels are still divided as to whether Tom Cruise's casting in 1994's Interview with the Vampire was genius or just ghastly.

Certainly, Rice herself was not pleased when Cruise was cast as tall (stop sniggering), sexy, and blonde vampire Lestat (apparently, she wanted British actor Julian Sands or Blade Runner's Rutger Hauer) and she gave a furious interview to the Los Angeles Times saying that Cruise was "no more my Vampire Lestat than Edward G Robinson is Rhett Butler".

Fans wrote petitions to complain about Cruise's casting, but it was all resolved after Anne Rice actually saw the finished movie. As well as calling Cruise to apologise, Rice paid for an advert to appear in Variety in which she urged fans to give the movie a chance (it went on to make over $200 million at the box office).

7. Sissy Spacek – Carrie White (Carrie)

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In Stephen King's horror novel, he describes 16-year-old Carrie White as "a frog among swans... she was a slightly chunky girl with pimples on her neck and back and buttocks, no one would call her attractive".

That's not exactly how you would describe Sissy Spacek, who played Carrie in the 1977 Brian De Palma-directed adaptation.

As well as being a former model, Spacek wasn't exactly a teenager when she got the part – she was 26 years old. In fact, even De Palma wasn't convinced she was right for the part and had Spacek audition for all the other female teen roles in the movie before allowing her to test for Carrie.

Years later, when she was interviewed for Inside the Actors Studio, Spacek remembered that she wore an old sailor dress to make herself look younger, and turned up to the audition without having washed her face and with Vaseline in her hair to make it look dirty. Her ploy worked – not only did she win the part, she was nominated for an Oscar, and the image of her, covered in blood at Carrie's prom, remains one of the most iconic in horror movie history.

8. Mark Ruffalo – The Hulk (Avengers Assemble)

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Best known for his roles in independent dramas like The Kids are Alright and Eternal Sunshine of the Spotless Mind, slimly built (and, erm, not exactly statuesque) Oscar-nominated actor Ruffalo didn't seem an obvious choice for the role of the biggest, angriest and greenest superhero on Earth – indeed, one Daily Telegraph writer described it as "either very bold, or very batty casting."

Of course, we all know that it turned out pretty well, with most fans of the Marvel character agreeing that Ruffalo's nervy, fun performance beats the Hulk's other recent and rather dull incarnations (Edward Norton, Eric Bana, we mean you) and is the best version of the angry green guy since Lou Ferrigno's '70s TV portrayal.

You can judge for yourself once more when Ruffalo's Hulk returns in Thor: Ragnarok at the end of October.

9. Robert Downey Jr – Tony Stark/Iron Man (Iron Man)

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Downey Jr's brilliant portrayal of billionaire Tony Stark in the Iron Man and Avengers movies (as well as, of course, this year's Spider-Man: Homecoming) has made him the lynchpin of the Marvel Cinematic Universe.

Hard to imagine, then, that back in 2007, he was considered a huge risk and director Jon Favreau had to beg Marvel to cast him.

While Downey Jr had won critical acclaim for roles in movies like Less Than Zero and Chaplin, by the late '90s he had become better known for his off-screen antics – cocaine addiction, driving under the influence, breaking into a neighbour's house and passing out on their bed – and was virtually unemployable since no movie studio could insure him.

It took Mel Gibson paying Robert's insurance himself for 2003's The Singing Detective to bring him back to the big screen, and Favreau's persuasive ways for him to go from Hollywood bad boy to comic-book hero/movie megastar.

From: Digital Spy