The MCU's commitment to getting proper actors to star in their movies rather than simply muscle-bound action men is best exemplified through Mark Ruffalo's take on Bruce Banner, aka Hulk. Despite being dwarfed in size standing next to the likes of Chris Evans and Hemsworth in full superhero regalia, Ruffalo holds his own in the role of the tortured scientist hiding the beast within. In an interview with Variety, Ruffalo admitted he still suffers from feelings of insecurity regarding his inclusion in the MCU

"Every time I'm whining like, "God damn, how long are we waiting for the set up?" I'm like, "Hey, Remember you're not even supposed to be here." Right. I just remember to be grateful because I still can't believe it. I still keep thinking, "They're going to throw me out of the club. I never belonged here in the first place and they're all going to find out."

The actor's entry into the MCU was itself something of an accident. Edward Norton had already made the first MCU movie, The Incredible Hulk, and established himself as the franchise's take on Bruce Banner. The movie underperformed at the box office, but Norton was perfectly willing to keep going with the role for future MCU movies.

However, the studio had other ideas. There were rumors that Norton was trying too hard to interfere with the writing, directing, and editing part of the movies. Such behavior would not do on the sets of 2012's The Avengers, which needed several A-list actors to work together without any ego clashes. Thus, Norton was removed from the role of Bruce Banner, and at the last hour, Mark Ruffalo was brought on in his stead.

Back then, Ruffalo was best known for supporting roles in mid-budget movies, few of which had the slightest whiff of the kind of action that would be required to be a part of the MCU. In fact, the actor admits that prior to entering Hollywood, he never dared imagine he would one day star as one of the main leads in a blockbuster franchise like the MCU:

"Never. We had this little theater and that was my dream come true. We were doing, like, 10 plays a year on Santa Monica Boulevard. I was bartending, but as shitty as the day could be, when I walked in the theater, I was in heaven. It's when I met Sunrise [Ruffalo's wife] and she was like, "I think you might be shooting a little bit low. I think you can probably expand what you think you're capable of."

Fortunately, Ruffalo listened to his wife and decided to take the plunge into what turned out to be an illustrious film career. The actor was last seen in the MCU in Avengers: Endgame, and is rumored to appear in some capacity in the Disney+ spinoff show She-Hulk. Ruffalo's high-profile Marvel journey has also netted him leading roles in smaller budget movies, from the critically-acclaimed Spotlight to the box-office smash Now You See Me. This news originated at Variety.