He was a Roman Emperor.
If You are talking about greek an roman gods, it is roman.
The Roman is Nereus; the Greek is Νηρευς
Apollo is Greek god not Roman.
Hephaestus is a Greek god not Roman.
Pegasus is both Greek and Roman.
It is a Greek myth if written by a Greek in Greek, or stated to be originating with the ancient Greek people. It is a Roman myth if written in Latin by a Roman citizen.
Persephone (Greek) Proserpine/Proserpina (Roman)Pan (Greek)Poseidon (Greek)Pluto (Roman)
Zeus was Greek. Jupiter was Roman.
Roman. Venus's Greek counterpart is Aphrodite.
Saturn is a Roman god not greek
Hera(Greek) Juno(Roman)
The blend of Greek and Roman cultures is referred to as Greco-Roman.