Post-credits scenes weren't a new thing in movies when the Marvel Cinematic Universe launched in 2008, but when Iron Man tacked on that extra minute of content, it kicked off a trend that has not only become one of this superhero movie franchise's defining features, it's since been adopted by other blockbuster franchises. As most of you can surely recall, Iron Man's post-credits scene saw Samuel L. Jackson's Nick Fury visiting Tony Stark at his mansion to talk to him about the Avengers Initiative. It was the first hint at a wider world of superheroes, but as director Jon Favreau admitted, this scene originally only meant to be a fun Easter egg for the hardcore Marvel fans in the audience. Favreau recalled:
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 it 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 (comic book) they recast him as Sam Jackson, and I thought that that would be a really good nod to the audience.
While Nick Fury has become one of the most recognizable characters in the MCU over the last decade, having Samuel L. Jackson portray the character at the end of Iron Man was definitely a deep cut at the time. I can imagine how casual moviegoers unfamiliar with Marvel Comics, let alone the Ultimate universe, might have been confused about what exactly was going on. Let's also not forget that before Iron Man, Nick Fury's biggest appearance outside the comics was the 1998 TV movie Nick Fury: Agents of S.H.I.E.L.D. I suspect not too many people remembered that movie, not to mention that David Hasselhoff's Nick Fury was modeled after the original comics Fury, not the Ultimate incarnation.
We were very careful how we selected the words. 'You're part of a bigger world now, 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.
On the off chance that folks didn't catch Nick Fury introducing himself to Tony Stark, Iron Man 2 brought them up to speed, and from there, Nick Fury served as one of the main connective threads between the MCU's Phase 1 movies. Fury was last seen aiding Earth's Mightiest Heroes in Avengers: Age of Ultron, but his whereabouts since then haven't been revealed.