From the introduction:
Demons are an integral part of the universe in which Angel takes place.
Before humanity arrived, demons ruled the world. The influence of demons was felt long after their civilization collapsed to make way for mankind. The Old Ones were driven from the world. Some plotted to regain their foothold on Earth while others became the Powers That Be and felt that the world belonged to man. Races of Lower Beings stayed on Earth, intermingling with the new forms of life. Some demons developed human-like societies. Some demons became hybrids with no small amount of human blood coursing through their demon veins. Then there are the vampires, demon spirits inhabiting human corpses.
Almost everything that Angel Investigations faces, both the good and the bad, is somehow connected to the legacy of demons. In fact, half of the Original Cast had a little bit of demon in them in one form or another. Demons will play an important role in any original adventures in which Players of the Angel RPG will participate. It's part of the genre.
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