The root of the idea of Mercury lies in Greek mythology with the messenger god, Hermes. The Romans, whose culture was in many ways derivative of the Greeks, borrowed the old stories and myths from the Greek God Hermes and laid them on top of their own similar god, Mercury. The process by which this was done is now shrouded somewhat by the mists of time, suffice it to say that these two names came to be recognized as designating one and the same mythical being. Mercury was one of the most popular of the ancient deities and was featured in many stories. He is supposed to have killed Argus on the orders of Zeus, by lulling him to sleep and then chopping off his head. He assisted Odysseus in his travels as that wanderer returned from the siege of Troy. It is interesting to note that Mercury generally does not act on his own but at the behest of some other god. He acts for his brother Apollo in saving the life of his child. Zeus often sends him to deliver dreams or to travel with a mortal to help keep him or her safe. This keeps him in accord with his mythical function as a messenger.
The way gods are handled in ancient myth does vary somewhat by storyteller and tale. However, the basic functions and personalities of gods treated in these stories remain relatively consistent. For example, in most myths we find the gods interfering directly in the affairs of humans largely without disguise. But in the Iliad, which is the Homeric story of the siege of Troy, we find the gods act in the guise of particular people, who are actually named. For example, in the famous scene where Priam goes to Achilles to beg for the return of the body of his slain son, Hector, the old king is guided by Mercury, but Mercury appears in the form of Polyctor, a soldier of Achilles. Hermes reveals himself, but he is also recognized by his kindness and a kind of aura surrounding him that protects Priam as he rides through the Greek army in a chariot loaded with treasures.
The Iliad is replete with such interferences by greek gods standing in the place of men. This way of giving the gods representation in the story might stem from the fact that the siege of Troy, though a heroic and ancient story, is based on factual occurrences. When the story was told and retold, there were people listening who had been at the battle, or at least they had heard stories from ancestors who had been there. The storyteller (Homer) had to trim his metaphorical sails a bit closer to the truth than the myth makers of a previous age, but still, make allowances for circumstances that seemed fortuitous.
The messenger god is generally described as wearing the clothes of a sheep-herd. He has winged sandals and sometimes a winged hat. He generally carries the caduceus which is a staff entwined with two snakes. The symbol for Mercury is shown at right. It may represent the caduceus staff or the circle might be Mercury’s head and the two “horns” might be the wings on his head.
Mercury was the son of Jupiter (king of the gods), the result of an illicit union with Maia, goddess of the clouds (as well as one of the Pleiades). His many adventures and his assignment as a guide of the dead to Hades made him the patron god of travelers. But his tricks also made him a patron of thieves. The Romans also made him the god of merchants and he lent his name to “mercantilism”. Wednesday was his day of the week.