The genius of Marvel's casting

'Iron Man 3' hits cinemas this week and marks Robert Downey Jr's fifth movie as Tony Stark – by now the role of the genius billionaire playboy philanthropist fits him like a... well, a suit. That's testament to Marvel's superb eye for casting – a knack that's netted them around $3.8 billion at the box office in the last five years. Since the start of Marvel's Phase One in 2008, the comic-company-turned-movie-studio has made a series of canny casting calls, beginning with Robert Downey Jr – a man previously thought of as unemployable.

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Marvel's approach to casting is indeed an interesting one. Famously, the studio 'lowball' their actors with a relatively small salaries to start out, with that figure rising with each subsequent, theoretical sequel. Perhaps more than any other movie studio, Marvel think in terms of the long game – the nine-picture deal that Samuel L Jackson signed after his Nick Fury cameo in 'Iron Man' is proof of their ambition. Anyone auditioning for a plum role in a Marvel movie will know that, should that movie be successful, more will follow: it's not just a part, it's a potential meal ticket.

With such a great track record, Marvel are well aware that they they can offer actors more than just money – they can offer them global fame. Take Chris Hemsworth, for example. The Aussie actor was an unknown when Kenneth Branagh hired him to play 'Thor' and though his initial salary was not exactly large in Hollywood terms (thought to be under $1 million), Marvel convinced Hemsworth that taking the role of  the God of Thunder would raise his profile, leading to more offers elsewhere – a higher rung on the industry ladder. They were right: Hemsworth has now worked with the likes of Ron Howard in 'Rush' and Steven Spielberg in the forthcoming 'Robopocalypse'. What's more, you can bet that his paycheque for 'Thor: The Dark World' will be significantly larger than his first.

Chris Evans – the man who wears the stars and stripes of Captain America – also represented a risk for Marvel. Just four years before he decorated himself in Old Glory, Evans was clad in the costume of a different superhero as 'Fantastic Four''s hot-headed Human Torch, Johnny Storm. Though initially worried that casting Evans as Cap would muddy their continuity, Marvel gambled that audiences would love him in the role as much as they did – and once again, they were proved right. Evans strikes the right balance between stoic patriotism and all-out cheesiness, and like his Avengers stablemates, it's difficult to imagine anyone else inhabiting their role quite as well.

Marvel learned how to play the casting game the hard way. Terrence Howard was the first actor to sign on to 'Iron Man' and was subsequently the highest-paid cast member. The studio changed their tactics after Howard came on board as Rhodey, and when it came to casting 'Iron Man 2', Marvel were not willing to meet his alleged salary demands, opting instead to recast the role with Don Cheadle on a lower wage but a better back-end deal.

Uniquely in Hollywood, Marvel have a different arrangement from other studios. Any actor that is given an audition must sign a 'take it or leave it' deal beforehand so they know what they're letting themselves in for – only when Marvel decide they've found their man does that deal become active. It allows them complete control over casting and alleviates the power struggles that come with contract negotiations. When Tobey Maguire held out for a rise for 'Spider-Man 2', citing back problems as his reason for stalling, Sony reportedly pursued Jake Gyllenhaal as a replacement Peter Parker, but really only used him as a pawn for a new deal with Maguire.

Marvel don't have a 100% perfect hit-rate – they struggled for years to find the right Hulk in Mark Ruffalo – but more than any other studio, they seem to have an uncanny habit of finding the right man for the part. They've made overnight stars out of Tom Hiddleston and Clark Gregg, and they'll continue to provide the foundations for many a career going forward. You only have to look back at their casting of Robert Downey Jr – then considered a huge risk, now one of the biggest stars in Hollywood – to see they know exactly what they're doing.