It wasn’t always tradition for comic-book movies to feature post-credits scenes. “Iron Man” kicked off the Marvel Cinematic Universe in general and that trope in particular, but according to director Jon Favreau, it wasn’t always part of the plan — in fact, it was actually “a bit of a lark” that it happened at all.
“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,” he tells Entertainment Weekly. “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. And Kevin [Feige, Marvel Studios executive] 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 world now, a bigger universe,’ and ‘the Avengers Initiative,’ laid breadcrumbs for what was to come,” Favreau continues. “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.”
Here’s the post-credits scene in question, which introduced the entire concept of the Avengers to moviegoers: