My sources are http://www.history.com/topics/ancient-history/greek-mythology, http://www.ancient.eu/Greek_Mythology/ and the book, ‘Ancient Civilizations’, published 2006 by McGraw Hill and National Geographic.
The ancient Greeks worshiped twelve gods and goddesses, Zeus, Hera, Hades, Poseidon, Aphrodite, among others. Multiple gods were common in ancient religions, dating back from the Mesopotamians and Egyptians. Each god was thought to control an aspect of nature or people’s lives.
Zeus ruled the sky and threw lightning bolts, the goddess Demeter made the crops grow, and Poseidon caused earthquakes. The Greeks sought the god’s favor and good fortune by performing rituals and building temples.
The mythology of the Greek gods started from oral traditions, but the first well-known origin story came from the poem Theogony written by Hesiod. The mythology of the gods became a religion and also as entertainment in stories and plays. The gods were essentially characters in drama, art and literature like Homer’s the Iliad and the Odyssey, and stories of Hercules, Achilles, Perseus and more.