Origins
Few words in English have undergone as complete a moral transformation as demon. Today it means pure evil. In ancient Greece, a daímōn was something closer to a guardian angel.
The Greek daímōn likely derives from a root meaning 'to divide' or 'to allot', making it originally a 'distributor of fate'. Homer used the word interchangeably with theos (god). Hesiod described daimones as the spirits of the Golden Age dead, watching over mortals invisibly.
Greek Origins
Socrates famously described his daimonion — a personal divine voice that steered him away from wrong decisions. This was no devil on his shoulder; it was conscience divinised. The Greek concept of eudaimonia, usually translated as 'happiness', literally means 'having a good daimon'.
The transformation began when Jewish scholars translated the Hebrew Bible into Greek, using daimonion for foreign gods and evil spirits. Christianity completed the reversal: all pagan spirits became demons. By the time the word entered English around 1200, the neutral Greek spirit had become exclusively evil.