In ancient Greek religion and mythology, the twelve Olympians are the major deities of the Greek pantheon, commonly considered to be Zeus, Poseidon, Hera, Demeter, Aphrodite, Athena, Artemis, Apollo, Ares, Hephaestus, Hermes, and either Hestia or Dionysus. They were called Olympians because, according to tradition, they resided on Mount Olympus.
Besides the twelve Olympians, there were many other cultic groupings of twelve gods.
In Greek mythology, deities referred to as chthonic (/ˈθɒnɪk/) or chthonian (/ˈθoʊniən/) were gods or spirits who inhabited the underworld or existed in or under the earth, and were typically associated with death or fertility. The terms chthonic and chthonian are derived from the Ancient Greek word χθών (khthṓn) meaning 'earth' or 'soil'. The Greek adjective χθόνιος (khthónios) means 'in, under, or beneath the earth', which can be differentiated from γῆ (gê), which refers to the living surface of land on the earth. In Greek, χθόνιος (khthónios) is a descriptive word for things relating to the underworld, which was in antiquity sometimes applied as an epithet to deities such as Hermes, Demeter, and Zeus.
The chthonic deities have been compared to the more commonly referred-to Olympic gods and their associated rites and cults. Olympic gods are understood to reference that which exists above the earth, particularly in the sky. Gods that are related to agriculture are also considered to have chthonic associations as planting and growing take place in part under the earth.