In Roman mythology, the messenger of the gods, equivelent of the Greek god Hermes.
In January-February 1944, after an accidental explosion in the city of Rome has awakened Mercury from his centuries-long sleep beneath the ruins of "what once was a temple dedicated to pagan rites," Mercury flies to America, where, more in pursuit of mischief than anything else, he leaves a trail of pandemonium in his wake and aids the cause of the Metropolis underworld by committing a series of mayhem-inducing pranks, as when he puts the city's police dispatchers to sleep with his magic staff and then sends all of Metropolis's police officers to chasing one another about the city by putting out a bogus radio call to the effect that bandits disguised as police officers are committing crimes using automobiles disguised as police cars. Superman ultimately apprehends the mischievous Mercury, however, and agrees to conceal his true identity from the population at large, thus sparing the winged god from the public humiliation of having been defeated by a mere mortal, in return for Mercury's promise to undo the trouble he has caused and to apprehend the criminals who have been aided by his antics (S No. 26/4: "The Quicksilver Kid!").
Mercury is among the many gods who grant Hercules magical super-powers, in the form of his famous sandals. "The first Olympus power from Mercury, the flying god, made winged sandals appear on my feet!" - muses Hercules (Act No. 267, Aug 1960: "Hercules in the 20th Century!"). (See: Hercules)
Mercury was one of the Olympians gods who lends his powers and abilities to Zha-Vam in an effort to teach Superman a lesson (Act No. 351, Jun 1967: "Zha-Vam the Invincible!").