The Book of Demons

Tolkien's The Lord of the Rings and an Arthurian role-playing game called Knights of the Round Table, Konstant and Perez decided to supply third-party supplements for the new role-playing game Dungeons & Dragons.

[1] Shannon Appelcline noted that Dungeons & Dragons was the clear market leader among about a dozen RPGs available by early 1977, by which time "third parties had begun supplementing the game, with the most notable early supplements including Wee Warrior's The Character Archaic (1975) and Palace of the Vampire Queen (1976), Little Soldier's The Book of Monsters (1976) and The Book of Demons (1976), and Judges Guild's City State of the Invincible Overlord (1976+) and Dungeon Tac Reference Cards (1976).

It would be 1977 or 1978 before "generic fantasy" supplements intended for D&D really started to proliferate, but even then, most would fit into the categories defined by these early publishers: accessories (like The Character Archaic), adventures (like Palace), monsters manuals (like Little Soldier's Books), and setting books (like City State).

Little Soldier did present some black magic rules in The Book of Demons, but that was a rare and much more focused exception.

Zocchi had originally planned to publish more, but the rest of the Little Soldier FRP books would have to wait until all six appeared as part of The Fantasy Gamer's Compendium (1983).