A franchise like the MCU which spans well over a decade and draws from several additional decades worth of storytelling across comics and cartoons is naturally a rich breeding ground for fan theories. Recently, Guardians of the Galaxy director James Gunn revealed on Twitter one particular aspect of his films in the franchise regarding Stan Lee that was directly inspired by a popular fan theory.
"Stan Lee's connection to the Watchers in Vol. 2 was definitely inspired by fan theories."
Marvel Comics legend Stan Lee has appeared in every movie in the MCU in one way or another, sometimes as a bus driver, other times as a guest at a party hosted by the Avengers. No explanation is ever given for the different characters Lee plays in each movie, all of whom mysteriously appear to always be found somewhere near a hero or a place where something dangerous is about to happen.
This led fans to speculate that Lee was playing the character of Uatu, the Watcher. In the comics, the Watchers are an ancient race of highly evolved beings tasked with observing and recording the history of the evolution of lesser species. Uatu is the Watcher assigned to Earth and has frequently interacted with the planet's heroes in the comics to stave off cosmic threats.
With the James Gunn sequel Guardians of the Galaxy Vol. 2, in a scene depicting interdimensional travel, the audience got a brief glimpse of Lee sitting on an asteroid in a spacesuit chatting with a company of Watchers. We get another glimpse of Lee in the same place at the end of the film, this time pleading with the watchers to arrange some form of transport for him off the asteroid.
The Guardians of the Galaxy scene confirmed that Lee, if not actually a Watcher himself, was at least someone who worked for them, and thus was far more powerful than his previous appearances in the MCU had let on. Fans were thrilled to see the long-standing fan theory embraced by the MCU, and Gunn proved that the showrunners at Marvel studios were indeed paying attention to the fandom. Back in 2017, Kevin Feige had also confirmed it was the fan theory that had inspired the idea of Lee's various characters turning out to be the same person working for the Watchers.
"Yes, we always thought it [the theory] would be fun. Stan Lee clearly exists, you know, above and apart from the reality of all the films. So the notion that he could be sitting there on a cosmic pit stop during the jump gate sequence in Guardians was something very fun ..."
"James had that idea and we shot that cameo and loved it so much, you know, you see it a couple of times in the movie. It wasn't in for a long time and we put it back in towards the end of the process where he references that time he was a Federal Express agent - we thought it would be fun to put that in there because that really says, 'So wait a minute, he's this same character who's popped up in all these films.'"