Stan Lee is the writer who along with some fantastic artists brought to life such great characters as Spider-man, the Fantastic Four, the X-Men, Daredevil, and so many more. What made his work so cutting edge at the time was he introduced to comics characters that were powerful yet flawed. They had problems or disabilities and this made them more naturalistic and complex.
He is 85 years old now, but in almost every Marvel movie they give him a small part. One of the fun things about watching the movies the first time is seeing where he might pop up. Someone has put together a compilation on You-Tube of many of them, which I've embedded below.
An interview with him about these appearances can be found here.