Originally, a demon isn't the red-skinned, evil, almost pop-culture seeming, horned beast that religions like Christianity has made it today. In Greek mythology, the word "demon" derives from the word Greek word "daimon" which essentially means that it's a godlike creature (If not a god on its own). Daimons served as a type of messenger to the Gods as a means of communication with the humans. An example of a common daimon messenger in Greek mythology is the Satyr.
Man, don't you hate when people think that demons are a Christian thing exclusively?
13👍 6👎