In the Heliopolitan Ennead cosmogony established in the sixth dynasty, Atum (Tem) was considered to be the first god, having created himself, sitting on a mound (benben) (or identified with the mound itself), from the primordial waters (Nu). Early myths state that Atum created the god Shu and goddess Tefnut from spitting or from his semen by masturbation in the city of Annu (the Egyptian name for Heliopolis), a belief strongly associated with Atum's nature as an hermaphrodite (hence his name meaning completeness). Strictly, the myth states that Atum ejaculated his semen into his mouth, impregnating himself, possibly indicating autofellatio, which has led many to misinterpret (Via euphemism or Bowdlerization) the myth as indicating creation from mucus.

Another belief held that Shu and Tefnut were created by Atum having sexual intercourse with a goddess, referred to as Iusaaset (also spelt Juesaes, Ausaas, Iusas, and Jusas, and in Greek as Saosis), meaning the great one who comes forth. She was described as his shadow. Consequently, Iusaaset was seen as the mother and grandmother of the gods.

In the Old Kingdom the Egyptians believed that Atum lifted the dead king's soul from his pyramid to the starry heavens.