Robert Downey Jr, best known for his role as Iron Man in the Marvel Cinematic Universe, will soon turn a shade darker to play Doctor Doom in the upcoming ‘Avengers: Doomsday’. While the star has now brought two major comic book characters to screens, according to him, there were two other characters that were difficult to adapt.In an interview with CBR, RDJ was asked which characters presented the greatest challenge for Marvel Studios president Kevin Feige and filmmakers Joe and Anthony Russo when adapting Marvel Comics storylines for the screen. Interestingly, he picked Captain America played by Chris Evans and Doctor Strange played by Benedict Cumberbatch, as the MCU’s toughest adaptations.Sharing his thoughts about the same, Downey said, “I still feel like the two hardest characters to pull off was what [Chris] Evans did with Cap.”He went on to explain, “And then, I think, [Benedict] Cumberbatch with Strange was like, ‘Are they really going to?’ Because in the comics, it works. And they were holding these spaces of credibility in the real world, and credibility in the world of magic and sorcery.”Captain America, as a hero, was only a super soldier, with a high moral compas and superhuman strength, his shield was his only defining factor, while Doctor Strange introduced mystical elements and alternate dimensions that expanded the MCU’s scope. Both characters ultimately became major characters of the franchise.Evans portrayed Steve Rogers across multiple Marvel films before handing the mantle to Anthony Mackie following the events of ‘Avengers: Endgame’, while Cumberbatch’s Doctor Strange has become one of the leading mentor figures in the current Multiverse Saga.Both Evans and Cumberbatch are set to return as their characters Steve Rogers and Stephen Strange in the upcoming ‘Doomsday’, with Downey is set to feature as the MCU’s next big villain, Doctor Doom.The trio is also expected to return in ‘Avengers: Secret Wars’ which is set to culminate the MCU’s Multiverse Saga’.