Jupiter (mythology) sibling Neptune
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, the Roman equivalents of Poseidon and Hades respectively. 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 identified with Jupiter. Tinia is usually regarded as his Etruscan counterpart.
brother or sister kin