The Improvised Iron Man Line Kevin Feige Instantly Loved

"I am Iron Man." It's one of the most famous lines in the Marvel Cinematic Universe, cementing Tony Stark as the world's most recognizable superhero. But when Robert Downey Jr. improvised those four little words at the end of 2008's "Iron Man," we had no idea how important it would be to the MCU.

In fact, it changed it forever.

"Tony Stark not reading off the card and not sticking with the fixed story? Him just blurting out 'I am Iron Man?' That seems very much in keeping with who that character is," said Marvel boss Kevin Feige (via IndieWire). "It just hadn't been done in the comics before, but it was something very much in keeping with the comics character and what he could have done."

Robert Downey Jr. went on to become the face of the MCU, suiting up as Iron Man in a total of 10 Marvel movies over 11 years. He is Iron Man. But more importantly, he gave Marvel the confidence to think outside the box. And as time went on, that improvised line became more important than ever.

Soon enough, Marvel had expanded way beyond Iron Man. By 2012, Marvel's heaviest hitters — Captain America, Hulk, Iron Man, and Thor — had all appeared in their own solo movies, culminating with their first super-powered team-up in "The Avengers." Even then, you could feel Iron Man's influence. Marvel was no longer worried about adapting its characters beyond what we had come to expect in the comic books.

"That success inspired us to go further in the trusting ourselves to find balance of staying true to the comics and the spirit of the comics but not being afraid to adapt and evolve and to change things," said Feige. "It's a fine line. If you're changing something for no reason, that's one thing, but if you're changing something because you want to double-down on the spirit of who the character is? That's a change we'll make."

Just look at "Thor," for example. When the film was released in 2011, I was surprised to find that the Norse god of thunder no longer tried to hide his identity. The comic books saw him take on the alter ego of Donald Blake while on Earth. But the MCU version of Thor no longer shied away from his destiny, only using the moniker as a gambit to escape S.H.I.E.L.D. custody.

"I am Thor, son of Odin," he eventually announced in "Avengers: Age of Ultron." But Iron Man's influence goes beyond heroes accepting their true identity.

Tony Stark next uttered his catchphrase at the end of "Iron Man 3" after destroying all his Iron Man suits. It was a declaration that he was more than just his armor, and he was right. By this point, he had emboldened Marvel to make increasingly big decisions when it came to its MCU storylines.

"I think it did inspire us on all the movies," said Feige. "What I love now — 20 movies in — is how fans expect the MCU to change and adapt. They expect us to be inspired by the comics as opposed to being slavishly devoted to them."

Enter the Mandarin in a bold departure from the comic books.

One of Iron Man's long-time adversaries, the Mandarin was the one we had been waiting for. I remember those first trailers, depicting him as a violent terrorist ... and couldn't have been more shocked when he turned out to be a caricature of a British thespian, played by the legendary Sir Ben Kingsley. The backlash was almost instant — how dare Marvel do this to us? But I have to admit, I loved it, and it was a big turning point for Marvel, too. The notion that they could change a famous villain so dramatically kept things fresh. As Feige put it so well, they were no longer expected to be "slavishly devoted" to the comic books. Even then, Marvel took a big risk when they toyed with the Mandarin.

But you know what? We never did see it coming.

The final time we heard Iron Man's trusty catchphrase was at the end of "Avengers: Endgame." The Avengers have assembled, but they've failed to take down Thanos. And as the mad Titan declares "I am inevitable," it looks as though all is lost.

Then, a harrowing twist sees Tony Stark make the noblest of sacrifices.

"And I am Iron Man," he says after wrestling the Infinity Stones from Thanos and snapping his fingers. It's one of the biggest moments in the MCU, with Iron Man saving the universe, causing Thanos and his forces to crumble into dust. But it's soon revealed that the "snap" has taken its toll on Stark ... and as he collapsed to the ground, there wasn't a dry eye in the house.

Ironically, Iron Man's final words almost didn't happen with the quick-witted Avenger originally scripted to be silent in that devastating moment. Thankfully, directors Joe and Anthony Russo had second thoughts:

"Tony used to not say anything in that moment. And we were in the editing room going, 'He has to say something. This is a character who has lived and died by quips.' And we just couldn't, we tried a million different last lines. Thanos was saying 'I am inevitable.' And our editor Jeff Ford, who's been with us all four movies and is an amazing storyteller, said 'Why don't we just go full circle with it and say I am Iron Man.' And we're like, 'Get the cameras! We have to shoot this tomorrow.'"

It's a poignant moment that underlines everything the MCU has become. He is Iron Man. And at that moment, we remember how Iron Man built the MCU, and gave Marvel the strength to go in new directions.