In ancient Greek religion, Agathos Daimon or Agathodaemon (Greek: αγαθος δαιμων, "very good spirit") was a daemon or presiding spirit of the vineyards and grainfields and a personal companion spirit, similar to the Roman genius, ensuring good luck, health and wisdom. Though he was little noted in Greek mythology (Pausanias conjectured that the name was a mere epithet of Zeus), he was prominent in Greek folk religion; it was customary to drink or pour out a few drops of unmixed wine to honor him in every symposium or formal banquet. In Aristophanes' Peace, when War has trapped Peace (Eirene) in a deep pit, Hermes comes to give aid: "Now, oh Greeks! is the moment when, freed of quarrels and fighting, we should rescue sweet Eirene and draw her out of this pit... This is the moment to drain a cup in honour of the Agathos Daimon." A temple dedicated to him was situated on the road from Megalopolis to Maenalus in Arcadia.

Agathos Daimon was the spouse or companion of Tyche Agathe ("Good Fortune"; Latin, and dialect, Agatha); "Tyche we know at Lebadeia as the wife of the Agathos Daimon, the Good or Rich Spirit." His numinous presence could be represented in art as a serpent or more concretely as a young man bearing a cornucopia and a bowl in one hand, and a poppy and an ear of grain in the other. The agathodaemon was later adapted into a general daemon of fortuna, particularly of the continued abundance of a family's good food and drink.

In the syncretic atmosphere of Late Antiquity, Agathodaemon could be bound up with Egyptian bringers of security and good fortune: a gem carved with magic emblems bears the images of Serapis with crocodile, sun-lion and Osiris mummy surrounded by the lion-headed snake Cnum-Agathodaemon-Aion, with Harpocrates on the reverse.