Robert Downey Jr. was concerned he played Iron Man for too long.

The 58-year-old actor portrayed Tony Stark and his superhero alter ego in 11 movies from 2008's 'Iron Man' to 2019's 'Avengers: Endgame' and he admitted he had reservations that playing the same character for such a long period could have affected his acting range.

Asked if he had concerns that playing the same role for so long would have an impact on his acting, he told the New York Times magazine: "Yes. A hundred percent, and I knew there was a point where Chris Nolan was endorsing, let’s work those other muscles, but let’s do it while rendering you devoid of your usual go-to things.

"It’s the fast-talking, charming, unpredictable, blah, blah, blah, or as my very close friend Josh Richman, a character actor, used to say, I made my bones playing 'Milo, the offbeat buddy.' And Milo, the offbeat buddy, better be offbeat!"

The 'Oppenheimer' star also admitted he had "reservations" about joining another potential franchise, playing animal expert Dr. Dolittle in 2020 flop 'Dolittle'.

He said: "I finished the Marvel contract and then hastily went into what had all the promise of being another big, fun, well-executed potential franchise in 'Dolittle.'

"I had some reservations. Me and my team seemed a little too excited about the deal and not quite excited enough about the merits of the execution.

"But at that point I was bulletproof. I was the guru of all genre movies."

But Robert - whose wife Susan produced 'Dolittle' - admitted there was a valuable lesson to be learnt from the project.

He explained: "Honestly, the two most important films I’ve done in the last 25 years are 'The Shaggy Dog' because that was the film that got Disney saying they would insure me.

"Then the second most important film was 'Dolittle', because 'Dolittle' was a two-and-a-half-year wound of squandered opportunity.

"The stress it put on my missus as she rolled her sleeves up to her armpits to make it even serviceable enough to bring to market was shocking. After that point — what’s that phrase? Never let a good crisis go to waste? — we had this reset of priorities and made some changes in who our closest business advisers were."