Minor SPOILERS ahead for Captain Marvel
In Marvel Studios' late Stan Lee was a prominent figure in the comic book world for decades, and when his characters began to be adapted to the big screen in some of Hollywood's biggest movies, the filmmakers found a way to pay homage to the icon. He's appeared in a number of Marvel movies across various film studios, but he's had a cameo in every single MCU property - from film to TV - dating back to 2008's Iron Man.
Lee has played a wide variety of bit roles across all 21 MCU movies, from a FedEx delivery man in Captain America: Civil War to a patient in a mental institution in Thor: The Dark World. Most of Lee's characters were unnamed, and portraying a Watcher Informant. However in Captain Marvel, Lee cameos as someone he's never played before in the MCU: Himself.
Related: Every MCU Movie Coming After Captain Marvel
Early on in Captain Marvel, the titular hero arrives on Earth and is tracking a Skrull, eventually being led onto a crowded train. Here, Carol closely scrutinizes each enger looking for the Skrull in disguise, and she happens upon a man reading a script. The man lowers the script to reveal Stan Lee. While it might appear he's playing just another actor in L.A., the title on the front of the script confirms he's playing himself - the script is for Kevin Smith's Mallrats. Released in 1995 (the year Captain Marvel takes place), Mallrats features Lee in a small role. Drawing the logical conclusion, the script confirms Lee is playing himself in Captain Marvel.
It's possible that one of Lee's past MCU cameos featured the comics legend as himself, but most of those roles were so nondescript it's impossible to know for sure. However, since his Captain Marvel cameo features Lee reading the script for a movie he really appeared in, that seems to confirm he's playing himself. Of course, that seems to throw a wrench in the theory that all of Lee's cameos are connected and he's playing one character across the whole MCU, one who reports back to the Watchers - an ancient race of aliens who watch and monitor the universe.
If, in the MCU, Stan Lee and the Watcher's Informant are the same - an immortal being who can appear relatively the same age between the 1940s and 2010s - then Lee would have looked the same from when he first became famous as a comic book writer until present day. Surely, someone would have noticed that a man as famous as Lee hasn't aged. Even if Lee and the informant aren't the same person, confirming Stan Lee exists in the MCU creates the question of how he became famous - he can't have created the characters who actually exist in the MCU, so did he create other comic book characters? Or is he famous for something else? This fictionalized version of Stan Lee must have done something to gain the attention of the MCU's Kevin Smith, or else why would the director want Lee to appear in Mallrats?
Ultimately, Lee's cameos in MCU movies are fun nods to the man who created many of the superheroes who star in this successful franchise. With cameos across all 21 movies, there simply may not be a way to make Lee's roles all connect and make sense within the continuity of the MCU. In the case of Lee's cameo in Captain Marvel, it's something a little different and a perfect hat tip to the film's 90s setting.
