Claim: Zeus is a god.

Jupiter , also Jove -LRB- Iūpiter -LSB- ˈjuːpɪtɛr -RSB- or Iuppiter -LSB- ˈjʊppɪtɛr -RSB- , gen. Iovis -LSB- ˈjɔwɪs -RSB- -RRB- , is the god of sky and thunder and king of the gods in Ancient Roman religion and mythology . Jupiter was the chief deity of Roman state religion throughout the Republican and Imperial eras , until Christianity became the dominant religion of the Empire . In Roman mythology , he negotiates with Numa Pompilius , the second king of Rome , to establish principles of Roman religion such as offering , or sacrifice .   Jupiter is usually thought to have originated as a sky god . His identifying implement is the thunderbolt and his primary sacred animal is the eagle , which held precedence over other birds in the taking of auspices and became one of the most common symbols of the Roman army -LRB- see Aquila -RRB- . The two emblems were often combined to represent the god in the form of an eagle holding in its claws a thunderbolt , frequently seen on Greek and Roman coins . As the sky-god , he was a divine witness to oaths , the sacred trust on which justice and good government depend . Many of his functions were focused on the Capitoline Hill , where the citadel was located . He was the chief deity of the early Capitoline Triad with Mars and Quirinus . In the later Capitoline Triad , he was the central guardian of the state with Juno and Minerva . His sacred tree was the oak .   The Romans regarded Jupiter as the equivalent of the Greek Zeus , and in Latin literature and Roman art , the myths and iconography of Zeus are adapted under the name Iuppiter . In the Greek-influenced tradition , Jupiter was the brother of Neptune and Pluto . Each presided over one of the three realms of the universe : sky , the waters , and the underworld . The Italic Diespiter was also a sky god who manifested himself in the daylight , usually but not always identified with Jupiter . Tinia is usually regarded as his Etruscan counterpart .