Stan Lee’s been appearing in Marvel-related adaptations since “The Trial of The Incredible Hulk” in 1989. To date he has made a humorous cameo in every installment of the Marvel Cinematic Universe leading some fans to theorize Stan Lee isn’t playing individual characters, he is, in fact, playing Uatu the Watcher. Watchers are extraterrestrial beings whose purpose is to monitor the activities of other species. Uatu is the Watcher assigned to observe Earth and its solar system. The theory makes sense when you look at the cameos Stan Lee has made that span several decades and places.
President of Marvel Studios Kevin Feige one remarked after “Guardians of the Galaxy Vol. 2”, “Yes, we always thought it would be fun. Stan Lee clearly exists, you know, above and apart from the reality of all the films.”