Zeus was the youngest son of Cronos and Rhea, and became the supreme ruler of all the gods of the ancient Greeks. Citizens from all of the Greek city-states honored him, particularly at the Temple of Olympus, which became the site of a major festival every four years - that religious festival eventually became known as the Olympic Games. A colossal golden statue of Zeus was the site of many rites and rituals involving the athletes of the Olympics.
Zeus was known as quite the philanderer. Although he was married to his sister Hera, goddess of marriage, he strayed from her bed fairly regularly. Zeus hooked up with numerous other goddesses, mortal humans, the occasional nymph, and even a few animals. Hera jealously put up with his wandering ways, and often took revenge upon Zeus' women by going after their children. Zeus sired many of the Greek heroes and demi-gods during his amorous adventures. His extramarital activities weren't limited to women, either. Zeus' cup-bearer, the handsome Ganymede, earned Hera's wrath when she discovered that the young man was also her husband's lover.
In addition to being the head honcho of Olympus, Zeus is the god of thunder and lightning. He is often represented by a lightning bolt, and is sometimes depicted with an eagle, bull, or oak tree. Although Zeus was venerated in many areas of Greece, there doesn't seem to be much consistency about the methodology of this worship, and his temples (and titles) took a variety of forms. A number of different "cults of Zeus" popped up throughout history. One common form of honoring him appears to be the sacrificing of a white animal -- sheep, bull, pig, etc. -- over an elevated altar.
As the supreme ruler of Mt. Olympus, Zeus was in charge of justice, morals and law. His word was to be obeyed by both men and gods alike. Today, many Hellenic Pagans continue to honor Zeus and the other gods of the ancient Greeks.
