A long time ago, in a movie galaxy far, far away, Tom Cruise was actively involved in trying to get a relatively unknown comic book character called Iron Man off the animation panels and into cinemas. Nowadays, its hard to picture anyone but Robert Downey Jr as Ol Shellhead, and his definitive portrayal has made it almost impossible for anyone to step into Tony Starks shoes without trembling. Nevertheless, at some point, replace him they must. The recent Avengers: Age of Ultron trailer and Captain America 3 rumours suggest that Earths Mightiest Heroes are set for some major changes, and as Marvels principal actors ages and contracts become more pertinent issues it surely wont be long before the casting couch gets a dusting off. Marvel are famously tough negotiators, so while Robert Downey Jr. was operating from a position of envious strength when he wrangled his monstrously well-paid current contract, things are a little different nowadays. In all likelihood, they now believe that their track record of success is such that they can afford to replace almost anyone without worrying that their empire will suffer any significant structural damage. So while the prospect of Leonardo DiCaprio playing Tony Stark is intriguing, it is unlikely that Marvel would be willing to meet his asking price. They could, of course, plump for complete unknowns when the time comes to find a new actor to wield Thors hammer or wear Nick Furys eye patch, but it seems more probable that they will seek a combination of experienced but affordable. Factor in the age issue and the pool of suitable talent diminishes somewhat further. So who might the likely candidates be if each actor were replaced tomorrow? Weve taken a shot at it and look forward to your angry comments decrying our shaky selections and advising who we should have chosen instead.