The very first superhero movie I ever saw was Spider-Man with Tobey Maguire. That movie got me into the idea that superheroes were so cool, and that there's a lot of really cool things that people can do with superhero movies. The creator of that character that I enjoyed so much was the late Stan Lee.
Stan Lee didn't just create Spider-Man. He assisted in the creation of many other Marvel superheroes that are still well-known and loved today. The Hulk, Thor, Iron Man, X-Men, Doctor Strange, Black Panther, the Fantastic Four, and more are comics and characters that he helped to bring to life alongside Jack Kirby, Steve Ditko, Bill Everett, and more.
His cameos were something that all Marvel Cinematic Universe fans came to expect and enjoy. A few of my personal favorites are these:
https://www.youtube.com/watch?v=iEuWx4fkrrE (he appears towards the end)
https://www.youtube.com/watch?v=TVoadkAMP4k (this one was more heartwarming, especially since he created Spider-Man)
https://www.youtube.com/watch?v=HnByuUqMeko (here are all Stan Lee cameos)
He was funny in interviews and these cameos, and he wrote such a sassy Spider-Man. There would be no funny end credit scenes in the MCU if not for him and his co-writers creating these hilarious and human characters.
"Heroes show us we don't need to be perfect to do what's right. It's not about living without fear, but facing injustice. It's not about being powerful but finding your calling when you least expect it. They show us it's okay to be vulnerable, no matter how tough you are because even though they're heroes, they're still human." -Stan Lee voiceover, Defenders Trailer
Stan Lee was famous for doing what he loved, and most people don't get to do what they love for a living, ever. He did what he loved and did it well, and became one of the most recognizable people in comic books and cinema. He made a difference in entertainment for so many people, and will for generations to come. While he may have passed away this morning, he is immortal in our hearts.