The daimon (δαίμων), also spelled daemon (meaning "god", "godlike", "power", "fate"), denotes an "unknown superfactor", which can be either good or hostile.

In ancient Greek religion and mythology a daimon was imagined to be a lesser deity or guiding spirit. The word is derived from Proto-Indo-European *déh₂i-mō ~ *dh₂i-mn-és 'divider, apportioner(?)'. Daimons were possibly seen as the souls of men of the golden age, tutelary deities, or the forces of fate.

Daimons are lesser divinities or spirits, often personifications of abstract concepts, beings of the same nature as both mortals and deities, similar to ghosts, chthonic heroes, spirit guides, forces of nature, or the deities themselves (see Plato's Symposium). According to Hesiod's myth, "great and powerful figures were to be honoured after death as a daimon…" A daimon is not so much a type of quasi-divine being, according to Walter Burkert, but rather a non-personified "peculiar mode" of their activity.^{[citation needed]}

In Hesiod's Theogony, Phaëton becomes an incorporeal daimon or a divine spirit, but, for example, the ills released by Pandora are deadly deities, keres, not daimones. From Hesiod also, the people of the Golden Age were transformed into daimones by the will of Zeus, to serve mortals benevolently as their guardian spirits; "good beings who dispense riches…[nevertheless], they remain invisible, known only by their acts". The daimones of venerated heroes were localized by the construction of shrines, so as not to wander restlessly, and were believed to confer protection and good fortune on those offering their respects.

One tradition of Greek thought, which found agreement in the mind of Plato, was of a daimon which existed within a person from their birth, and that each individual was obtained by a singular daimon prior to their birth by way of lot.

Homer's use of the words theoí (θεοί, "gods") and daímones (δαίμονες) suggests that, while distinct, they are similar in kind. Later writers developed the distinction between the two. Plato in Cratylus speculates that the word daimōn (δαίμων, "deity") is synonymous to daēmōn (δαήμων, "knowing or wise"); however, it is more probably daiō (δαίω, "to divide, to distribute destinies, to allot").

In Plato's Symposium, the priestess Diotima teaches Socrates that love is not a deity, but rather a "great daimōn" (202d). She goes on to explain that "everything daimōnion is between divine and mortal" (202d–e), and she describes daimōns as "interpreting and transporting human things to the gods and divine things to men; entreaties and sacrifices from below, and ordinances and requitals from above..." (202e). In Plato's Apology of Socrates, Socrates claimed to have a daimōnion (literally, a "divine something") that frequently warned him—in the form of a "voice"—against mistakes but never told him what to do. The Platonic Socrates, however, never refers to the daimonion as a daimōn; it was always referred to as an impersonal "something" or "sign". By this term he seems to indicate the true nature of the human soul, his newfound self-consciousness. Paul Shorey sees the daimonion not as an inspiration but as "a kind of spiritual tact checking Socrates from any act opposed to his true moral and intellectual interests."

Regarding the charge brought against Socrates in 399 BC, Plato surmised "Socrates does wrong because he does not believe in the gods in whom the city believes, but introduces other daemonic beings..." Burkert notes that "a special being watches over each individual, a daimōn who has obtained the person at his birth by lot, is an idea which we find in Plato, undoubtedly from earlier tradition. The famous, paradoxical saying of Heraclitus is already directed against such a view: 'character is for man his daimon'".