We usually think of history changing in big, splashy ways. A war, an election, what have you. It’s the same with movies. If I asked you to name a movie that made history, you might come up with something like ‘Star Wars’, something that wasn’t just a box office hit but one that sparked an enduring cultural phenomenon. By that standard, ‘Iron Man’, would certainly make the cut. But while Iron Man’ was undeniably a major hit (unexpectedly so, for that matter) and kicked off the decade-spanning, billion-dollar juggernaut that is the Marvel Cinematic Universe, the film’s greatest historical contribution had to be its post-credit scene.

You know the scene. After dodging SHIELD representatives (chiefly Clark Gregg’s Agent Coulson) throughout the film, Tony Stark finds Nick Fury (played by Samuel L. Jackson, because of course) waiting for him in his office, ready to discuss “the Avenger Initiative.” While the MCU wouldn’t have existed (at least as we’ve come to know it) had ‘Iron Man’ flopped, it was this tag scene that really established it as a universe that extended not only beyond Iron Man himself but even beyond Iron Man’s movies. It wasn’t the first post credit scene ever or even the first in a superhero movie, but it was the first to have such wide-ranging implications not only for the film’s characters but ultimately for the film industry as a whole.

But what went into making that happen? As the world braces for the arrival of ‘Avengers: Infinity War’ – the culmination of a filmmaking experiment that began with ‘Iron Man’ and continued through seventeen intervening films – those involved have been taking a look back at where it all began. Speaking to Entertainment Weekly, ‘Iron Man’ director Jon Favreau reminisced on how the fateful stinger scene came to be and how the nascent Marvel crew approached it:

“That was a bit of a lark. I wanted to include Easter eggs that the fans would appreciate and we thought the idea of a post-credit scene could be fun. It was something that wasn’t really in the script originally. But I thought the idea of Nick Fury being Sam Jackson would be really fun, because when Nick Fury  was reimagined in ‘The Ultimates’ they recast him as Sam Jackson, and I thought that would be a really good nod to the audience. And Kevin [Feige] was way into it, too. Kevin really lit up. We worked on that dialog together. We were very careful how we selected the words. “You’re part of a bigger universe,” and “the Avengers Initiative,” laid breadcrumbs for what was to come. We had the idea that we would somehow group these characters together, that was part of what would happen, but a lot of things had to go right for that to happen, so  we were really just laying out a basic mission statement of purpose, to show our intent, and thinking that the few people who would linger in the theater would be the ones who would appreciate it most.”

As mission statements go, it was certainly an ambitious one. It’s easy to forget, but the Marvel model of shared universe movies had never been done prior to that first cycle of films, and it’s a success that frankly has yet to be replicated. Though in retrospect, what made that first stinger scene so effective – in a way that, again, has arguably not been replicated since – is that very deliberate choice of words that Favreau mentions. When Nick Fury says that “you’re part of a bigger universe,” he’s not just speaking to Tony Stark. He’s speaking to the audience.

Directed by the Russo brothers from a script by Christopher Markus and Stephen McFeely, ‘Avengers: Infinity War’ marks the culmination of a decade-long effort by Marvel Studios and sees the Avengers team up with the Guardians of the Galaxy to take on Thanos. The film counts Robert Downey Jr., Scarlett Johansson, Mark Ruffalo, Tom Holland, Karen Gillan, Paul Rudd, Chadwick Boseman, Benedict Cumberbatch, Elizabeth Olson, Sebastian Stan, and three gentlemen named “Chris” among its gargantuan cast. The long awaited movie is set to arrive in theaters on April 27, 2018.