The whole MCU started with Robert Downey Jr., and with his contract running out soon, it will probably have to avoid ending with him. Downeys portrayal of Tony Stark has been the charismatic lynchpin that the rest of the universe has gravitated around. People got to Marvel films just to see Downey in the role he was born for, and he excels in it. And even if he signs a new contract, it's just delaying the inevitable; t some point age will catch up with him and force him out of the centre of Marvels universe. Of course, Marvel have previous experience with replacing actors. They swapped Edward Norton for Mark Ruffalo and Terence Howard for Don Cheadle, and neither change led to any great deal of protest. However, theyve never had to replace anyone quite as integral to the MCU as Downey, Jr., and theres no telling how audiences would take it. As far as a lot of people are concerned, Downey, Jr. is Tony Stark and no-one else could take over. Fans could easily reject the new guy, or he could struggle to escape from Downeys gigantic shadow, leading to all sorts of problems and possibly even the death of the MCU. And leaving Iron Man behind is equally problematic. How Marvel plan to change their lead actors (since the others are coming to the end of their contracts, too) remains to be seen. However they do it, they need to be careful. If theyre not, they'll alienate the fans, and everything theyve worked so hard to build could come crashing down. What do you think could kill the Marvel Cinematic Universe? Do you feel that its invincible and could go on for ever? Do you agree or disagree with any points raised here? Let us know in the comments, and thanks for reading.