Who is Zeus in greek mythology?

Zeus was king of the gods and goddesses in Greek mythology.

Zeus, the youngest son of Cronus and Rhea (Cronus and Rhea were both 'Titans', the beings before the gods), he was the supreme ruler of Mount Olympus and of the Pantheon of gods who resided there. Being the supreme ruler he upheld law, justice and morals, and this made him the spiritual leader of both gods and men. Zeus was a celestial god, and originally worshiped as a weather god by the Greek tribes. These people came southward from the Balkans circa 2100 BCE. He has always been associated as being a weather god, as his main attribute is the thunderbolt, he controlled thunder, lightning and rain.

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Zeus is the son of Cronos and Rhea. He occurs in all strata of Greek mythology, beginning as a vegetation spirit annually slain and resurrected, and ending up as king and father of all the Olympian gods. See the Oxford Classical Dictionary for some of the the details of his career.