First let me state that I think Mr. Matheson is a very great writer. I read several of his short stories and they are quite scary and creepy. I can see how he inspired Stephen King with these works. Matheson wrote several episodes for The Twilight Zone, which include one of my favorites, "Nightmare at 20,000 feet".
Yes, a young William Shatner
Several of his books have been adapted to film. One that completely shocked me, considering he is a horror/sci fi author is his adapted film "Somewhere in Time". I couldn't believe it when I read it. I love that film and think it is one of the most beautiful love films. That's a book and film review for a different day.