No, Stephen King and Dean Koontz have never collaborated to write a book together. Both authors are prominent figures in the horror and suspense genres, but their writing styles and themes are quite distinct, which likely contributes to their decision to pursue solo writing careers.
Stephen King is known for his rich character development and immersive storytelling, often exploring themes of fear, childhood, and the supernatural. On the other hand, Dean Koontz blends elements of horror with science fiction and fantasy, focusing on the battle between good and evil, and frequently incorporating philosophical reflections.
While they have mutual respect for each other as authors, their works remain separate, each showcasing their unique voice and perspective. Fans of both writers can appreciate the individual contributions they have made to literature, even though a collaboration between them has never come to fruition.