Mark Ruffalo
Mark Ruffalo will appear in “Avengers: Infinity War” as Hulk, but his character will not have a standalone film. Pictured: Ruffalo took part today in the Walt Disney Studios live action presentation at Disney's D23 EXPO 2017 in Anaheim, California on July 16. Getty Images/Alberto E. Rodriguez

Robert Downey, Jr. and Mark Ruffalo played the Iron Man and Hulk, respectively, in Marvel’s iconic movie, “The Avengers.” There had been several behind the movie scenes that went viral over the past years and one of the most epic reveal has something to do with their costumes —well, the Hulk’s costume to be specific.

Planet Hulk
Hulk’s storyline in “Thor: Ragnarok” will adapt the Planet Hulk storyline from the comic books. Marvel

Marvel has made a lot of improvements with the movie over the years, especially with “The Avengers’” suits. While fans are enjoying these superheroes’ fancy costumes on the big screen, they have little idea how they really looked like behind the flashing cameras.

Ruffalo, who played the role of Hulk (the green giant with temper issues) shared how painfully funny it was to wear Hulk’s costume. Ruffalo said, in a talk with GQ, that it was so humiliating, Digital Spy reported. Then reportedly went on saying that whenever he walked around, all the other actors would start laughing because he wore “ridiculous” pajamas that made him look like Chinese checker boards while they [other “Avengers” actors] wore these super cool costumes.

Ruffalo also shared how Downey reacted seeing his awkwardly looking costume. Downey, who played the role of Iron Man in “The Avengers” reportedly said he had a lot of compassion for Ruffalo, pointing out his realization seeing how hard it was for his pal to be in the costume all day.

Avengers 4 trailer
The "Avengers 4" trailer is rumored to release Wednesday night at a fan event, but Marvel Studios has not confirmed that. Marvel Studios

There was this one time, as Ruffalo recalled, when he had to do a scene with Downey where his character, the Hulk, had to catch Iron Man. He did the “Hulk roar” in those little PJs and Downey, while having his eyes closed, opened just one and said the hilarious response, “really Ruffalo? That’s what you’re really going with?”

Avengers Endgame box office Avatar
"Avengers: Endgame" is now $15.5 million away from topping "Avatar." Marvel Studios

Ruffalo was the third actor who played the Hulk. His predecessors were Eric Bana (2003) and Edward Norton (2008). It is note-worthy that the previous “Hulk” movies were not well-received by the viewers so it was a bit of a challenge for Marvel to find a new one because “The Avengers” cannot be just done without a Hulk.

Because of “The Avengers” producer Joss Whedon, Ruffalo was reportedly offered to play the character of Bruce Banner —yes, he is the Hulk’s human alter ego and vice versa— but he was hesitant. Ruffalo was reportedly unsure to accept the role because he had doubts of playing the character right, the Blast reported.

In addition, at that the time, there was no official script yet. Ruffalo reportedly made a promise to himself not to sign in any movie without a script. Despite his doubts, Whedon was pretty convinced he could it. But the producer’s encouragement did not suffice.

Enter Downey.

All it took was one call from the guy who played the billionaire Tony Stark for Ruffalo to say yes. Downey reportedly said, “Come on, Ruffalo,” when he called his pal followed by “we got this,” and that was it.

Robert Downey Jr.
Robert Downey Jr. will play Iron Man/Tony Stark in "Captain America: Civil War." Pictured: Downey attends the European premiere of "Avengers: Age of Ultron," on April 21, 2015. Reuters