Stan Lee is one of the titans of comic book literature:
In collaboration with several artists, most notably Jack Kirby and Steve Ditko, he co-created Spider-Man, the Hulk, the X-Men, the Fantastic Four, Iron Man, Thor, and many other fictional characters, introducing complex, naturalistic characters and a thoroughly shared universe into superhero comic books.
Hence, even if you don’t read comic books, you’ve probably heard of his work. What you might not be aware of is that he has frequent cameos in movies:
In the first Hulk movie (at 1:06 above), he is shown together with Lou Ferrigno who played the Hulk in the 1970s Hulk TV show. Lou Ferrigno also has a cameo in the second Hulk movie.
Lee makes a cameo appearance as a man interviewed by the media about his opinion concerning the Avengers thwarting the Chitauri's attack on Manhattan Island. Lee's character responds with, "Superheroes in New York? Give me a break", and then returns to a game of chess with a fellow senior citizen.