Atum (or Tem or Tum) was an early god of Heliopolis, and a predynastic sun-deity. The Heliopolitan theologians interpreted his name to mean the "complete one." A reference to their belief that Atum created himself out of the waters of Nun, either through the effort of his own will power or by uttering his own name, which was the power of the spoken word. He also was called Neb-er-djer, "Lord to the Limit" or Universal God.
He was founder of the Heliopolitan Ennead, and was called Bull of the Ennead, a reference to his cult animal, the bull Mnevis. Sometimes Atum was thought to have originated as a serpent in Nun, and to be destined to return to that form; but through his identification with Re, serpents became his enemies. At times he was represented with an head of an ichneumon, because once when a serpent attacked him, he turned himself into an ichneumon to devour it.
More commonly, however, he s represented as a bearded man, usually aged and tottering to the western horizon as the setting sun. Because he is seen as the creator of the gods and men, and hence of the divine order of heaven and on earth, he was called Lord of the Two Lands and as such was depicted as wearing the pschent, the double crown of Upper and Lower Egypt, and bearing an ankh scepter, the sign of life and symbol of royal authority.
Originally Atum was androgynous, and as Iusau the sole parent of the first divine couple, Shu and Tefnet; but he was later given two wives, Iusau and Nebhet Hotep. A.G.H.
Grimal, Pierre, Larousse World Mythology, Secaucus, New Jersey, Chartwell Books, 1965, pp. 30-31
Ions, Veronuca, Egyptian Mythology, Feltham, Middlesex, Hamlyn Publishing Group, Ltd., 1968. p. 40