Gray Barker published UFO literature from his country outpost in Exchange, (outside of Clarksburg) West Virginia from 50s until his death in 1984.
He published a book by Al Bender in 1955ish called "The Three Men" (something like that) that was about Bender (A self proclaimed UFO researcher) being visited by 3 men dressed in black claiming to be from the government (or another planet, can't remember) telling him he was too close to the truth about UFOs and to back off or else. They drove a black car, had black sun glasses, black suits, etc, etc, etc. Bender was so frightened that he abandoned the UFO field for good and disappeared never to speak of this experience again. I believe Bender, up to the point of being visited by The Men In Black, had some kinda UFO research club.
This was the first appearance in UFO lore of The Men In Black.