"The Latin form of the Greek name Zeus, the national god of the Greeks, and the supreme ruler of the heathen world," says Fallows. The people at Lystra called Paul Mercury, because he was the chief speaker, and Mercury was the god of eloquence; Barnabas, who was with Paul, they named Jupiter, the god whom they worshiped (Acts 14:12).
According to The New International Encyclopædia, Jupiter was the chief god of Latin mythology, identified by the Romans with the Greek Zeus. He was worshiped by the Greeks and the Romans as the god of light and the heavens, whence come the fructifying showers and also the destructive storms and deadly lightning. Especially was he looked on as the wielder of the thunderbolt. He was the god that all other gods had to obey because he was stronger than any of them. Thus he was the supreme god of both gods and men. Jupiter is a contraction of Zeus pater, or Jove father.