The Greek gods constantly interfered in the affairs of humanity. Artemis - goddess of the hunt and healing - could also bring plague. The Iliad is loaded with references to the gods doing this or that to sway a battle or to convince a human to act. Even when their activities seemed to have nothing to do with humans, they could have tremendous repercussions, as when Demeter - the goddess of agriculture - grieved for the three months every year that her daughter Persephone had to spend in the underworld with Hades.
The stories surrounding the ancient Greek gods are myths that originated as a means of explaining the natural world. When the Greeks first settled around the Peloponesus they had not yet produced the great philosophers Socrates, Democritus, and Aristotle. They had no knowledge of the sciences. When some phenomena occurred, they felt compelled to explain it. This was a way of somehow controlling or understanding it. When an earthquake occurred, they had no knowledge of plate-tectonics, so they used a familiar image, a great man or god whom they named Poseidon and imagined that he, by a stamp of his huge foot could cause havoc on the Earth.
Attributing such dangerous, as well as positive phenomena to gods, the Greeks felt they could, control events by influencing the god in question. They might pray to the god, or pour wine on the ground, burn sacrifices, hold revelries in honor of the god, build a statue, or any number of other activities that might appease or help the god.
Having no knowledge of biology, when a plague struck one of their small city states, they might attribute it to the arrows of Apollo - the god of archery and the sun. Fervent prayers and burnt offerings would be made, and eventually the plague would pass. Since human nature is inconstant, there was continually reason to believe that the people were alternately in and out of favor with their gods. Paradoxically, this would spur even more devotion.
The attributes of the invented gods were strikingly human. Dionysus - the god of wine, for example, was a reveler more concerned about his own immediate gratification than about respect for others or for the future. And Cronus - the titan - was depicted as coveting power so much that he devoured his own children to prevent their overthrowing him, after all he had overthrown his own father at the behest of his mother Gaia.
The gods were thought by the Greeks to be immortal, but this does not mean that they could not be harmed. Ares - the God of War - was wounded by the actions of Athena during a battle in the Trojan War. Hephaestus - the god of the Forge - was thrown from mount Olympus by his mother Hera. He landed so hard he became a cripple. His relationship with his wife Aphrodite - the goddess of love - would also leave him crippled emotionally.
The mythology surrounding the Greek gods became so important to society that it was made the basis for the education of youth. The myths became vital for understanding Greek poetry and prose. The mythology was transported and translated throughout the civilized world, first in the conquests of Alexander and then in the expansion of Rome. The Romans had pretty much adopted Greek mythology as their own, only renaming many of the characters. Zeus the king of the gods became Jupiter, Athena became Minerva, and Hermes, the messenger god became Mercury.
This broad influence of the Greek gods in the ancient world, and the high respect in which that culture has been held ever since, has made the study of Greek mythology an important subject even today, where references in literature to these gods and goddesses abound. An understanding of mythological characters can be very useful in understanding ideas, themes, titles, and characters even of literature being produced today.