The Nommo are ancestral spirits (sometimes referred to as deities) worshipped by the Dogon people of Mali. The word Nommos is derived from a Dogon word meaning "to make one drink." The Nommos are usually described as amphibious, hermaphroditic, fish-like creatures. Folk art depictions of the Nommos show creatures with humanoid upper torsos, legs/feet, and a fish-like lower torso and tail. The Nommos are also referred to as “Masters of the Water”, “the Monitors”, and "the Teachers”. Nommo can be a proper name of an individual, or can refer to the group of spirits as a whole. For purposes of this article “Nommo” refers to a specific individual and “Nommos” is used to reference the group of beings.
Dogon mythology says that Nommo was the first living creature created by the sky god Amma. Shortly after his creation, Nommo underwent a transformation and multiplied into four pairs of twins. One of the twins rebelled against the universal order created by Amma. To restore order to his creation, Amma sacrificed another of the Nommo progeny, whose body was dismembered and scattered throughout the universe. This dispersal of body parts is seen by the Dogon as the source for the proliferation of Binu shrines throughout the Dogons’ traditional territory; wherever a body part fell, a shrine was erected.
In the latter part of the 1940s, French anthropologists Marcel Griaule and Germaine Dieterlen (who had been working with the Dogon since 1931) were the recipients of additional, secret mythologies, concerning the Nommo. The Dogon reportedly related to Griaule and Dieterlen a belief that the Nommos were inhabitants of a world circling the star Sirius (see the main article on the Dogon for a discussion of their astronomical knowledge). The Nommos descended from the sky in a vessel accompanied by fire and thunder. After arriving, the Nommos created a reservoir of water and subsequently dived into the water. The Dogon legends state that the Nommos required a watery environment in which to live. According to the myth related to Griaule and Dieterlen: "The Nommo divided his body among men to feed them; that is why it is also said that as the universe "had drunk of his body," the Nommo also made men drink. He gave all his life principles to human beings." The Nommo are also thought to be the origin of the first Hogon.
In the 1970s a book by Robert Temple titled The Sirius Mystery popularized the traditions of the Dogon concerning Sirius and the Nommos. In The Sirius Mystery, Temple advanced the conclusion that the Dogon’s knowledge of astronomy and non-visible cosmic phenomenon could only be explained if this knowledge had been imparted upon them by an extraterrestrial race that had visited the Dogon at some point in the past. Temple related this race to the legend of the Nommos and contended that the Nommos were extraterrestrial inhabitants of the Sirius star system who had travelled to Earth at some point in the distant past and had imparted knowledge about the Sirius star system as well as the Solar System upon the Dogon tribes.