Greek Gods
Worship of gods and religious practices varied widely in ancient Greece and came in both the form of popular public worship and cult religions. However despite the many variations, there were many beliefs and practices that were shared by most people.
There were fourteen major gods and goddesses that were worshiped by people throughout ancient Greece, they were; Zeus, Apollo, Artemis, Poseidon, Hera, Aphrodite, Dionysus, Athena, Hephaestus, Ares, Hermes, Hades, Hestia and Demeter. Zeus was the dominant figure as the king of the gods and the others usually were attributed dominance over some aspect of nature. Poseidon was thought to rule over the sea and earthquakes and Hyperion was in control of the sun, others were attributed to more abstract concepts, like Aphrodite, the goddess of love.
Although the gods were immortal and very powerful, they still had to obey fate, for example after the Trojan War, Odysseus was fated to return to his home in Ithaca and even the gods could not prevent this from happening, though they did lengthen the journey and make it more difficult for him.
The Greek deities took on human form, acted like them, had human vices and even had babies with them sometimes. Often, gods would oppose each other and side with different armies during a war and some were associated with specific cities such as Athena and Athens, Apollo with Delphi and Delos and Zeus with Olympia. Some were even associated with non-Greek states like Poseidon with Ethiopia and Troy and Ares with Thrace.
As well as the main gods there were lesser deities who where related to the major gods, for example Dionysus the god of wine and spiritual ecstasy who was the son of Zeus. On occasion, humans could become gods, Heracles, who was the son of Zeus but had a mortal mother was offered the position of god after performing great heroic deeds but rejected it, though he did accept the offer of immortality.
Ceremonies and rituals were usually performed at alters and were devoted to one or more gods. Food and precious items would be left at the alter and sometimes animals would be sacrificed, with the flesh eaten and the offal burned as an offering to the god or gods being worshipped. Great temples were built in honour of the gods, most notably the Temple of Zeus at Olympia and the Parthenon in Athens, dedicated to Athena. Some temples employed oracles who were believed to be able to see the future, the most famous of which was the Delphic oracle at the Temple of Apollo in Delphi.
Aside from the main public religions there were the mystery religions or cults which hand picked its members for initiation. From the Hellenistic period, these cults became more popular all over the Greek Empire. Some were new like the Mithras cult while others were hundreds of years old, like the Egyptian mysteries of Osiris.
Not everyone believed in many gods, some like Plato believed in the existence of one supreme god who he believed to be perfect and his student, Aristotle, argued that as no empirical evidence for the gods could be found, only a creator god must exist that took no further interest in the universe or the lives of men.