The 48-year-old President of Marvel Studios admits that his company owes much of its recent success to the Hollywood star, who debuted as Tony Stark in the original 'Iron Man' film in 2008.
He reflected: "I was lucky enough to be involved in early 'Spider-Man' films and 'X-Men' films. But we wanted to do an 'Iron Man' movie. And I do think, still, the biggest risk - which seems outrageous to say now - was casting Robert Downey Jr.
"It was both the biggest risk and the most important thing in the founding of the Marvel Cinematic Universe. Without Robert, we wouldn't be sitting here today. I really believe that."
Kevin always recognised that Robert was an "amazing actor". However, he admitted casting him as Iron Man required a leap of faith.
He told CinemaBlend: "He was an amazing actor. Everybody knew he was amazing actor. But he hadn't been an action star.
"He wasn't a marquee star, necessarily. And we quickly realised the risk, I've said this before, was not casting him. And Jon Favreau really had that vision for that movie and for Robert in that role.
"That decision, and the success of that decision, I think empowered us with further risks and further choices."
Robert previously admitted that while his days of playing Iron Man are now over, he remains "eternally grateful" for the opportunity.
He said: "I've done all I could with that character and can do other things now.
"Now, being middle-aged, you start looking at the back nine and realise this is all part of the journey, and things end. I am fortunate and eternally grateful to have wound up where I have."
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