Whitley Streiber?
I always liked Streiber's books. It's as though he knew and had experienced enough to know there was some weird connection between covert military programs – nobody called it 'Deep State' back then – and the demonic.
He couldn't quite put his finger on it, but the fiction he produced helped people get acquainted with the general lay of the land in this subject area. And it's been quite helpful for many people's Qresearch.