Earlier this week, there was a nasty little rumour going around that Orlando Bloom was in talks to play Bruce Wayne and therefore Batman in the upcoming Man Of Steel sequel. Now, while Bloom is not necessarily a bad actor (discuss), he's definitely not someone we'd see going toe to toe with Henry Cavill and it looking in any way believable. This got us thinking about previous examples of when Hollywood just got it plain wrong when it came to choosing their leading men and women. And here they are, in no particular order, our Ten Biggest Casting Mistakes In Movies.

COLIN FARRELL – ALEXANDER

Farrell is a perfectly capable actor given the right set of circumstances, but playing a genius war tactician with surfer-dude blonde locks are not those circumstances. Maintaining the Irish accent throughout also didn't help much.
Who Should Have Played The Part: Leonardo DiCaprio, especially since he was to be the lead in the Baz Luhrmann take of the tale, which was shut down once Farrell's version lost so much money at the box office.

JULIA ROBERTS – OCEAN'S ELEVEN

When surrounded by the likes of Clooney and Pitt and Damon, the character of Tess needed to be an object of desire, and painfully cool. Roberts is a lot of things, but desirable and cool are not two of her biggest attributes.
Who Should Have Played The Part: Maybe Catherine Zeta-Jones, who did a much better job of playing a cool object of desire in Ocean's Twelve.

RALPH FIENNES – MAID IN MANHATTAN

Released around the same time he was playing a shark-toothed serial killer in Red Dragon, Ralph Fiennes is a great actor, but he doesn't exactly come to mind when you think of the words "romantic" and "comedy". We kept waiting for him to bite Jennifer Lopez's face off.
Who Should Have Played The Part: A posh, unimposing toff? Was Hugh Grant unavailable?

HAYDEN CHRISTENSEN – ATTACK OF THE CLONES / REVENGE OF THE SITH
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There has been evidence that Christensen can in fact act – see Shattered Glass for proof – but he failed spectacularly under the weight of this semi-Shakespearean tragic character. Whether it was him or George Lucas he kept pushing for more childish temper tantrums, this was just one epic fail spread over two movies.
Who Should Have Played The Part: If he'd been around at the time, Ryan Gosling. Otherwise… James Franco?

DENISE RICHARDS – THE WORLD IS NOT ENOUGH

Yes, she was hot, and looked totally at home in those shorts. And if her character was a professional shorts wearer, then we'd have no problem. But Richards was playing a nuclear physicist, and forgive us, but when it comes to a higher end IQ and actually knowing rocket science….. No. Just no.
Who Should Have Played The Part: Producers originally wanted Sharon Stone for the role that eventually went to Sophie Marceau, so just cast Sophie in Denise's role instead. Donezo.

HALLE BERRY – CATWOMAN

Something happens to an actress when she wins an Oscar, in that she follows it up with tripe. Charlize Theron followed Monster with Aeon Flux, Hilary Swank followed Million Dollar Baby with The Reaping, and Berry followed Monsters Ball with … this. Somehow there was some confusion between Catwoman being an empowered antihero with being a slutted out stripper, which Berry went all out for, and came away looking like it was all her fault.
Who Should Have Played The Part: In this movie? Preferably nobody. But gun to our heads, Jessica Alba.

KEANU REEVES – CONSTANTINE

In the comic books, John Constantine is blond and from Liverpool who is constantly battling his own demons and teetering on the edge of sanity. Reeve's is both (a) none of those things, and (b) incapable of acting like he is any of those things. Not that the movie was bad, but Reeves was almost definitely the worst part of it.
Who Should Have Played The Part: Michael Fassbender, now. Or maybe Paul Bettany, at the time.

NATALIE PORTMAN – V FOR VENDETTA

Suffering from the same problems that Jodie Foster has in Elysium, Portman is a fantastic actress who was simply crippled by her own attempts at an accent. Her wide-berth impersonation of what a British person sounds like almost completely undoes all of the good work she had otherwise put into the role.
Who Should Have Played The Part: Carey Mulligan. Oh, she wasn't around much then? Well then, Samantha Morton.

LEONARDO DI CAPRIO – GANGS OF NEW YORK

While he wasn't alone in the miscasting stakes for this movie (see also: Cameron Diaz), Di Caprio simply couldn't nail the accent, plus he was far too pretty to be taken a serious threat to Day Lewis. That violent, murderous instinct just wasn't present in him. Yet.
Who Should Have Played The Part: A violence prone Irish man? Colin Farrell. These two should've just done swapsies with Alexander and be done with it.

SOFIA COPPOLLA – THE GODFATHER: PART III

If ever there was a single piece of evidence that proves nepotism is a bad, bad thing, then this is it. Director Francis Ford Coppolla casting his daughter in a key role for the final chapter of his epic trilogy was a big mistake, and while its failure to live up to its predecessor's standards can't be left entirely at her feet, she was a big BIG part of what was wrong with that movie.
Who Should Have Played The Part: Apparently Madonna auditioned for the role, and we never thought we'd live to see the day we'd say this, but she would've been a better fit.

Special Mentions:
Elijah Wood in Green Street.
Keira Knightley in Domino.
Vince Vaughn in Psycho.
Jessica Alba in Fantastic Four.
John Wayne (as Genghis Khan!) in The Conqueror.
Got any you think we've missed? Comment below!