In the ancient Greek religion and Greek mythology, the Twelve Olympians are the major deities of the Greek pantheon, commonly considered to be Zeus, Hera, Poseidon, Demeter, Athena, Apollo, Artemis, Ares, Aphrodite, Hephaestus, Hermes, and either Hestia or Dionysus.Hades and Persephone were sometimes included as part of the twelve Olympians (primarily due to the influence of the Eleusinian Mysteries), although in general Hades was excluded, because he resided permanently in the underworld and never visited Olympus.
The Twelve Olympians, also known as the Dodekatheon (Greek: Δωδεκάθεον from δώδεκα,dōdeka, "twelve" and θεοί, theoi, "gods"), were the principal deities of the Greek pantheon, said to reside atop Mount Olympus. The Olympians gained their supremacy in a ten-year-long war of gods in which Zeus led his siblings to victory over their predecessor gods, the Titans.
The concept of the "Twelve Gods" is older than any extant Greek or Roman source. The gods meet in council in the Homeric epics, but the first ancient reference to religious ceremonies for the Olympians collectively is found in the Homeric Hymn to Hermes. The Greek cult of the Twelve Olympians can be traced to 6th-century BC Athens and probably has no precedent in the Mycenaean period. The Altar of the Twelve Gods at Athens is usually dated to the archonship of the younger Pesistratos, in 522/521 BC.