Hermes was the messenger god in Greek Mythology. He is a protector of travelers, shepherds and thieves.
Hermes follows the archetype of the trickster. He was frequently potrayed to be witty and charismatic, but also a liar and a thief. Even as an infant, he exhibited these traits. Hermes secretly crawled away from Mount Cyllene and stole some of Apollo's cattle, cleverly disguising their tracks. Some versions of the myths say that he put shoes on their feet, while others say that he made the cows walk backwards.
Hermes sacrificed some of the cows to give to the Olympian gods, in order to gain their attention and favour. The Homeric Hymn to Hermes credits Hermes with the invention of fire during this sacrifice. After the sacrifice, Hermes returned home, and found a tortise along the way, which he also sacrificed. He used the cow's intestines and the shell of the tortise to create the first lyre.
Feigning ignorance to his mother, he convinced Maia that he was not to blame for the theft of the cows. Zeus intervened, and forced an agreement between the two. During the argument, Hermes began to play the lyre that he had created. Apollo, enchanted by the music, agreed to allow Hermes to keep the cattle in exchange for the instrument. (Apollo is often depicted holding the lyre.)
Hermes also serves as a psychopomp, one who guides the dead to the afterlife — Hades' Underworld. Hermes was one of the few gods who could safely travel back and forth between the Underworld and the world of the living.
The Roman equivalent of Hermes is Mercury.