For the ancient Greeks, Poseidon (left) was the god of the sea. For the ancient Romans, Neptune (below) was the god of the sea. Generally speaking, Greeks and Romans accepted Neptune and Poseidon to be different names for the same god. The same qualities were attributed to Neptune as to Poseidon (e.g. both were believed to be the god of horses as well as of the sea, and both were believed to wield tridents.If you were to ask a Hindu, ancient or modern, "Do you believe there is a god of the sea who is also the god of horses, wields a trident and is named Neptune or Poseidon?" you would probably be told, "Of course not. Varuna is the god of water and the celestial ocean, and the god of underwater law. He wields a snake in the form of a noose."
If you were to ask a Christian, Jew or Muslim, of any age and from any age, "Do you believe in Neptune, Poseidon or Varuna?" the answer would probably be along these lines: "No. There's no god of the sea. No god of this or that or the other. There is only one god, the god of Everything and every thing."
But if you asked, "do you believe that a god made the seas and oceans and rivers?" the answer might be "yes, the god made all things, wet as well as dry!" And if you asked an Ancient Greek, an ancient Roman or a Hindu the same question you would get a similar answer. Except that the Hindu might say, "It's not important whether it's a god or the god. Why not have both? Why not have many gods in one god. Varuna is a god, yes. But he is also a particular aspect of Brahman, the fundamental ground of Reality. The Russians have nested dolls. We have nested gods!"
To this day some people believe that god is an older man with a long white beard sitting on a cloud. The attributes of that conception of god include the gender, the age, the beard, position (sitting) and location (in the sky, on a cloud). As well, there is a hidden attribute: existence.
Do you believe in God?" is a stupid question. "Do you believe that God [insert attribute/s]?" is a more productive question because it at least enables a discussion on what the attributes of God may or may not be. Another example of the ship of meaning crashing into the rocks of language.