Typically, Stephen King has little-to-no involvement in the creative process of movies and TV shows adapted from his works. He provides the source material that that other screenwriters and directors take over, and the author rarely has a say in whether these fellow storytellers honor or change his text around. With 1989’s Pet Sematary, however, King played a bigger role than usual. Specifically, he wrote the screenplay, which allowed him to build a relationship with director Mary Lambert and, inevitably, he ended up on the set in costume for a small but key role.
Article source: https://www.cinemablend.com/news/2483035/the-8-best-stephen-king-cameos-in-tv-shows-and-movies-adapted-from-his-books