11. Muhammad Ali
Could The World's Greatest have been a believable component of Earth's Finest? He did go on to fight Superman in comic form, but he almost got a chance to play the character on screen before that happened. What Happened? There was a period in the 1970s when Ilya and Alexander Salkind were trying to get Superman made that it looked unlikely that they'd ever be able to sort out the excruciatingly complex issue of rights with DC, which is perhaps why they went a bit mad with who should play the titular hero. For a while, the producers entertained the idea of bringing in Ali, despite his lack of experience in acting. Would He Have Worked? As Superman, unquestionably, thanks to his physique and that super-human spirit he already exuded, but it's hard to imagine The Greatest toning himself down to play Clark Kent. Occasionally, in his more reflective moments, Ali's vulnerability did shine through in interviews - particularly in times of turmoil - but there's not exactly a very grand history of sportsmen taking up acting roles that required a strong acting performance. And the lasting caveat that should always come with that suggestion is the ominous memory of what Vinnie Jones did to Juggernaut in X-Men: The Last Stand.