Hermes was the son of Zeus, king of the gods, and a nymph named Maia. Immediately after birth he invented the lyre from a tortoise shell, as well as stealing his brother Apollo's herd of cattle. The last was accomplished more with guile and dark humor than malice. This amoral cleverness would become a defining trait of Hermes.
Hermes soon became the herald of Zeus, and a special guide for those under Zeus' protection. It is in this capacity he appears in both The Iliad and The Odyssey. Hermes was also thought to lead shades, or souls of the recently dead, to the waiting ferryman at the River Styx. He was the only god that could easily traverse the boundaries between earth, Olympus and Hades.
Hermes was celebrated early in cult as the patron of travelers, heralds and herdsman. A phallic stone pile bearing his likeness, called a Herm, was erected at the boundaries of property lines as an apotropaic talisman. At a later date he also became a patron of the gymnasium, and the athletics and rhetoric that was taught there.
Hermes had few temple cults but was celebrated generally in everyday life of the Greeks. In the Hellenistic age he was conflated with Thoth, the Egyptian scribe god of magic. This conflated Hermes-Thoth (called Hermes Trismegistus, or Hermes Thrice-Great) would later become a mythological front for an occult movement in late Antiquity known as Hermeticism.
The deity Mercury had a temple on the Aventine and a festival celebrated on May 15th. Mercury, like Hermes, was the god of circulation - of people, goods and words. Under Greek influence it seems the two gods were linked early on, with the myths of Hermes being transferred to that of Mercury. His cult was established in very early Rome to solicit divine protection of the emerging grain trade. From there he became one of the principle deities of negotiatores, or Roman businessmen.
Roman literature, inspired closely by Homeric epic, has Mercury performing as a divine herald and guide at the behest of Jupiter. The magic and humorous duplicity of Mercury is also present. A "mercurial" personality became proverbial, and Augustus himself was unfavorably portrayed with such a personality by Horace.
In the Western provinces, the Roman Mercury was equated with a variety of local Celtic deities who shared some of Mercury's attributes. The most widespread candidate was a god called Lugh, who like Mercury had many talents. In the East, Mercury took over Hermes' association with Thoth, providing a powerful figurehead of magic for cabals of occult practitioners.
In the modern imagination Mercury is still a sigil of travel and communication. Ford has named one of its models of cars after him, while the Greek post office uses Hermes as its symbol.
This article was written by forum member Ursus
Hornblower and Spawforth. The Oxford Classical Dictionary
Walter Burkert. Greek Religion
Homer. The Homeric Hymn to Hermes.