Jupiter was the king of all the gods. Mercury was his youngest son. Mercury's mother was Maia.
Mercury had many talents. He could fly faster than most of the other gods, partly because of his winged sandals. He was also trustworthy. He was playful enough to be interesting. He was very bright and very loyal. He was the best negotiator in the world. He was always cracking deals to get himself and others out of trouble.
Unlike his half-brother, Ares, the god of war, whom almost none of the other gods liked very much, Mercury was very popular in the ancient heavenly world. Even Ares trusted him. For that matter, even Jupiter trusted him. Jupiter was always sending his youngest son, Mercury, off to fix some problem or other. And Mercury almost always did.