In Greek mythology, Hermes was the son of Zeus and Maia and was the god of speech, eloquence, trade and travel. He was known as a trickster god and is the patron deity of thieves. This is no doubt because in the myths, he stole his brother Apollo's prized cattle when he was only a day old. Apollo was furious but Hermes soon invented the lyre using the shell of a tortoise and gifted it to his brother, whereupon he was promptly forgiven. 

Illustration by Jay Sibbick
Hermes most important role was as the messenger of the gods. He was also a psychopomp who guided souls to the afterlife and was the only Olympian who could cross the border between the living and the dead. Hermes was well loved by all the gods and featured in many of the myths including those of Persephone, Perseus, Pandora, Paris and Achilles. 

'Souls on the Banks of the Acheron' - Adolf Hiremy-Hirschl, 1898 (detail).
In classical and modern art, Hermes is depicted as beautiful youth, often with winged sandals and cap and holding his caduceus. However, in archaic art he is shown as a mature bearded man. In ancient Greece stone herms were used to honor Hermes, who was originally a phallic god connected with fertility. They were placed at boundaries and were thought to ward off evil. In Roman mythology he is known as Mercury.

A collection of art featuring the god Hermes (or Mercury):

'Mercury' - Peter Paul Rubens, 1577.
W. B. Richmond, 1886.

'Mercury with His Symbols' - Hendrik Golzius.
'Souls on the Banks of the Acheron' (depicting Hermes in the underworld) - Adolf Hiremy-Hirschl, 1898.

'Hermes, Herse and Aglauros' - Paolo Caliari, ca. 1580.

'Mercury' - Everlyn de Morgan, 1870-1873.

'The Friendship of Apollo and Hermes' - Noel Coypel.

Hermes with his maother Maia - Detail of Attic vase, ca. 500 BCE.
Attic Red Figure - ca. 480 BCE.
Archaic bearded Hermes from herm, early 5th century BCE.

Hermes Ingenui (Vatican Museum) - 2nd Century BCE Roman copy of 5th Century BCE original.

One of my favourite books about Hermes is 'Quicksilver' by Stephanie Spinner, which is a lovely re-telling of the myths in which Hermes is involved from his perspective.