People in ancient Greece believed in many gods: they were polytheistic (PA-lee-thee-ISS-tick). It is impossible to say how many Greek gods there were, because different Greek people worshipped different gods, or called their gods by different names. Certainly there were hundreds of gods and goddesses. The most famous of these gods, and the ones which the most people sacrificed to, were Zeus, Hera,Apollo, Artemis, Poseidon, Aphrodite, Athena, Demeter, Hermes, Ares, and Hades.
But there were many others: Asclepius, the god of medicine, Persephone, Demeter’s daughter, Gaia the earth goddess, Hecate, and so forth.
In addition, every little village had its own gods. The local stream, an especially big oak tree, an oddly shaped rock, all were thought to have their own god inside them, who had to be worshipped or he or she would get mad. It was, as Keith Hopkins has said, “a world full of gods.”
Greek people also worshipped foreign gods, if they thought other people’s gods might help them somehow. The Egyptian goddess Isis was especially popular in Athens in the Hellenistic period, for instance. And many Hellenistic Greeks worshipped Astarte, too.