A friendly spirit of Ancient Greece, literally a 'good demon' or 'noble spirit'. He protected people and their homes, but had a particular fondness for vineyards and farmer's fields. He was often portrayed as a perfectly normal young man, but could also be represented as a snake. In his human form he was often represented as carrying a cornucopia and bowl in one hand and an ear of corn and a poppy in the other. He wasn't a major player in written Greek mythology, but was quite popular in folk mythology. He was seen as a friendly house and field spirit to whom one could make small offerings of wine to help insure good luck and good health. He did, however, have at least one temple dedicated to him, built on the road travelling from Megalopolis to Maenalus in Arcadia.

He was also known as Agathos Daimon or Agathodaemon (the Greeks, actually, were inclined to call him ἀγαθὸς δαίμων). He was married to the much more famous Tyche Agathe (Τύχη Ἀγαθή) commonly referred to as simply Tyche, who was the spirit of good fortune that protected cities.

In later years he was absorbed into the Roman goddess Fortuna, who took over the role of Tyche. He managed to keep his own name in Egypt, where he was seen as a snake with a human head, but remained as a spirit bringing good fortune.

Agathodemon is sometimes considered to be the antonym of cacodemon, although both cacodemon and its more commonly recognized antonym eudemon are general classes, rather than a specific entity.