Hermes (/ˈhɜːrmiːz/; Ancient Greek: Ἑρμῆς) is an Olympian deity in ancient Greek religion and mythology considered the herald of the gods. He is also widely considered the protector of human heralds, travelers, thieves, merchants, and orators. He is able to move quickly and freely between the worlds of the mortal and the divine aided by his winged sandals. Hermes plays the role of the psychopomp or "soul guide"—a conductor of souls into the afterlife.

In myth, Hermes functions as the emissary and messenger of the gods, and is often presented as the son of Zeus and Maia, the Pleiad. He is regarded as "the divine trickster", about which the Homeric Hymn to Hermes offers the most well-known account.

Hermes's attributes and symbols include the herma, the rooster, the tortoise, satchel or pouch, talaria (winged sandals), and winged helmet or simple petasos, as well as the palm tree, goat, the number four, several kinds of fish, and incense. However, his main symbol is the caduceus, a winged staff intertwined with two snakes copulating and carvings of the other gods.

In Roman mythology and religion many of Hermes's characteristics belong to Mercury, a name derived from the Latin merx, meaning "merchandise", and the origin of the words "merchant" and "commerce."

The earliest form of the name Hermes (Ἑρμῆς) is the Mycenaean Greek *hermāhās, written 𐀁𐀔𐁀 e-ma-a₂ (e-ma-ha) in the Linear B syllabic script. Other forms of the name of Hermes are Hermeias (Ἑρμείας), Hermaōn (Ἑρμάων), Hermān (Ἑρμᾱν), Hermaios (Ἓρμαιος), and Hermaỵos (Ἓρμαιυος). Most scholars derive Hermes from Greek ἕρμα (herma), 'stone heap'. Hermax, ('heap of stones'), hermaīon, ('gift of Hermes'), hermaīos hill were holy to Hermes.

The etymology of ἕρμα itself is unknown, but is probably not a Proto-Indo-European word. R. S. P. Beekes rejects the connection with herma and suggests a Pre-Greek origin. However, the stone etymology is also linked to Indo-European *ser- ('to bind, put together'). Scholarly speculation that Hermes derives from a more primitive form meaning 'one cairn' is disputed. Other scholars have suggested that Hermes may be a cognate of the Vedic Sarama.

It is likely that Hermes is a pre-Hellenic god, though the exact origins of his worship, and its original nature, remain unclear. Frothingham thought the god to have existed as a Mesopotamian snake-god, similar or identical to Ningishzida, a god who served as mediator between humans and the divine, especially Ishtar, and who was depicted in art as a caduceus. Angelo (1997) thinks Hermes to be based on the Thoth archetype. The absorbing ("combining") of the attributes of Hermes to Thoth developed after the time of Homer amongst Greeks and Romans; Herodotus was the first to identify the Greek god with the Egyptian (Hermopolis) (Plutarch and Diodorus also did so), although Plato thought the gods were dissimilar (Friedlander 1992).

His cult was established in Greece in remote regions, likely making him originally a god of nature, farmers, and shepherds. It is also possible that since the beginning he has been a deity with shamanic attributes linked to divination, reconciliation, magic, sacrifices, and initiation and contact with other planes of existence, a role of mediator between the worlds of the visible and invisible. According to a theory that has received considerable scholarly acceptance, Hermes originated as a form of the god Pan, who has been identified as a reflex of the Proto-Indo-European pastoral god *Péh₂usōn, in his aspect as the god of boundary markers. The PIE root *peh₂ 'protect' also shows up in Latin pastor 'shepherd' (whence the English pastoral). A zero grade of the full PIE form (*ph₂usōn) yields the name of the Sanskrit psychopomp Pushan, who, like Pan, is associated with goats. Later, the epithet supplanted the original name itself and Hermes took over the role of psychopomp and as god of messengers, travelers, and boundaries, which had originally belonged to Pan, while Pan himself continued to be venerated by his original name in his more rustic aspect as the god of the wild in the relatively isolated mountainous region of Arcadia. In later myths, after the cult of Pan was reintroduced to Attica, Pan was said to be Hermes's son.