Greek mythology consists of an extensive collection of narratives detailing the lives and adventures of a wide variety of gods, goddesses, heroes, and heroines, which were first envisioned and disseminated in an oral-poetic tradition. Our surviving sources of mythology are literary re-workings of this oral tradition, supplemented by interpretations of iconic imagery, sometimes modern ones, sometimes ancient ones, as myth was a means for later Greeks themselves to throw light on cult practices and traditions that were no longer explicable. The historian must sometimes deduce from hints in imagery, such as in vase paintings, and offhand references the recognition of mythic themes tacitly expressed in cult practice.
In the wide variety of Greek legends and stories, the ancient gods all appear in human form: the few chimerical beings such as the Sphinx all have Near Eastern or Anatolian origins. Despite the fact that many Gods have birth myths attributed to them, none of them ever age. No sicknesses affect them, and there are precious few ways to wound a god. They have the ability to conceal themselves from human beings, they can transport themselves anywhere in the blink of an eye, and they are able to speak through people without their knowledge. Each god possesses a distinct appearance, descends from his or her own geneology, pursues differing interests, has a certain area of expertise, and is governed by a unique personality; however, these descriptions arise from a multiplicity of archaic local variants, which do not always agree with one another. When these gods were called upon in poetry, prayer or cult, they are referred to by a combination of their name and epithets, that identify them by these distinctions from other manifestations of themselves. A Greek deity's epithet may reflect a particular aspect of that god's role, as Apollo Musagetes is "Apollo, [as] leader of the Muses." Alternatively the epithet may identify a particular and localized aspect of the god, sometimes thought to be already ancient during the classical epoch of Greece.
In such mythic narratives, we are told that the gods are all part of a huge family, spanning multiple generations. The oldest of the gods were responsible for the creation of the world, but younger gods usurped their power. In many familiar epic poems set in the "age of heroes," the twelve Olympians are said to have appeared in person. In order to help out the Greeks' primitive ancestors, the gods performed miracles, instructed them in various areas of practical knowledge, taught them proper methods of worship, rewarded good behaviour and chastised immorality, and even had children with them.