Have read a Dean Koontz book (w/c I forgot the title) and looks to me that it has some similarity with Stephen King's work..They have the (in some ways) same topic like involving writers/authors in a state of fascination towards their characters to the extent of putting them into life as themselves..
but I think Stephen King has been around for sometime..his book, I remember was made into movies since late 70's..take "Carrie" starring the then young Sissy Spacek and John Travolta as a supporting role..I doubt if "Rage Carrie" (the sequel) was also based on Stephen King's book..
All I can say is that both authors have pretty eerie imaginations that my friend stopped reading a Koontz book bec. it gave her nightmares??!?..