Zeus was King of the Ancient Greek gods of Mount Olympus as well as the god of thunder and lightning. The Romans conflated Zeus with their own king of the gods Jove Pater (Jupiter). "Zeus" and "Jove" are both believed to be derived from the Proto-Indo-European name Dyauṣ.
According to tradition, Zeus was the youngest son of the Titans, Cronus (Kronos in old style) and Rhea. An oracle had foreseen that a son of Cronus would overthrow him. In response, Cronus swallowed all of his children seconds after their birth. Only Rhea's trickery saved Zeus, who grew up to defeat his father, liberate his swallowed siblings, and become King of the Gods.
Zeus was famous for his lechery. His dalliances produced many of the heroes of Greek myth, including Perseus and Hercules. However, he also expressed a strong fondness for Prince Ganymede of Troy, which may or may not have included a homosexual element.
Zeus tasked Andromeda with vanquishing the Gorgons, three women whose beauty was causing great consternation to Mount Olympus. She later married his son Perseus. Zeus attended the wedding and lusted after the serving maids, and even the serving men whom he mistook for Ganymede.
After several centuries of Christianity as the dominant religion of Greece, Zeus apparently ceased to exist for want of worshipers - or possibly he was still there on top of Mount Olympus but no longer daring to venture into the world. The SatyrAmpelus gloated that while the mighty Zeus was no longer having sexual adventures with human women, he - a mere Satyr - was still doing so at every opportunity. George the Shoemaker thought that the widespread reading of Homer might be enough to lend the old Olympian gods a kind of half life, even when nobody worshiped them any more - since even loyal Christians could not help believing in these gods while reading the vivid text of the Iliad and Odyssey. For the same reason, such clergymen as Bishop Eusebius would have liked to replace the reading of Homer with the Gospels. However, Homer was too deeply entrenched in the Greek and Roman culture to be dislodged by the Church.
The question of Zeus' status (living or dead) is unanswered in this novel. However, in The Case of the Toxic Spell Dump which is probably set in the same universe, and takes place in the 1990s, his close relations Poseidon and Hermes survive. According to the rules of henotheism set forth in the novels, it would be unlikely for the lesser gods to survive their leader's death by any great span of time. In Case, narrator David Fisher fleetingly references Zeus as Jove, but does not make clear whether he is alive or dead at that time.