Aten also Aton, Atonu, or Itn (Ancient Egyptian: jtn, reconstructed [ˈjaːtin]) was the focus of Atenism, the religious system established in ancient Egypt by the Eighteenth Dynasty pharaoh Akhenaten. The Aten was the disc of the sun and originally an aspect of Ra, the sun god in traditional ancient Egyptian religion. Akhenaten, however, made it the sole focus of official worship during his reign. In his poem "Great Hymn to the Aten", Akhenaten praises Aten as the creator, giver of life, and nurturing spirit of the world. Aten does not have a creation myth or family but is mentioned in the Book of the Dead. The worship of Aten was eradicated by Horemheb.

The solar Aten was extensively worshipped as a god in the reign of Amenhotep III when it was depicted as a falcon-headed man much like Ra. In the reign of Amenhotep III's successor, Amenhotep IV, the Aten became the central god of the Egyptian state religion, and Amenhotep IV changed his name to Akhenaten to reflect his close link with the new supreme deity. The principles of Aten's religion were recorded on the rock tomb walls of Akhetaten. In the religion of Aten (Atenism), night is a time to fear. Work is done best when the sun, Aten, is present. Aten cares for every creature, and created a Nile river in the sky (rain) for the Syrians. Aten created all countries and people. The rays of the sun disk only holds out life to the royal family; everyone else receives life from Akhenaten and Nefertiti in exchange for loyalty to Aten. Aten is depicted caring for the people through Akhenaten by Aten's hands extending towards the royalty, giving them ankhs representing life being given to humanity through both Aten and Akhenaten. In Akhenaten's Hymn to Aten, a love for humanity and the Earth is depicted in Aten's mannerisms:

Aten bends low, near the earth, to watch over his creation; he takes his place in the sky for the same purpose; he wearies himself in the service of the creatures; he shines for them all; he gives them sun and sends them rain. The unborn child and the baby chick are cared for; and Akhenaten asks his divine father to 'lift up' the creatures for his sake so that they might aspire to the condition of perfection of his father, Aten.

Akhenaten represented himself not as a god, but as a son of Aten, shifting the previous methods of pharaohs claiming to be the embodiment of Horus. This contributes to the belief that Atenism should be considered a monotheistic religion where "the living Aten beside whom there is no other; he was the sole god".

There is only one known instance of the Aten talking, "said by the 'Living Aten': my rays illuminate…"

Aten is an evolution of the idea of a sun-god in Egyptian mythology, deriving a lot of his concepts of power and representation from the earlier god Ra but building on top of the power Ra represents. Aten carried absolute power in the universe, representing the life-giving force of light to the world as well as merging with the concept and goddess Ma'at to develop further responsibilities for Aten beyond the power of light itself.

Aker was first depicted as the torso of a recumbent lion with a widely opened mouth. Later, he was depicted as two recumbent lion torsos merged with each other and still looking away from each other.

From Middle Kingdom onwards Aker appears as a pair of twin lions, one named Duaj (meaning "yesterday") and the other Sefer (meaning "tomorrow"). Aker was thus often titled "He who's looking forward and behind". When depicted as a lion pair, a hieroglyphic sign for "horizon" (two merged mountains) and a sun disc was put between the lions; the lions were sitting back-on-back.

In later times, Aker can also appear as two merged torsos of recumbent sphinxes with human heads.

Aker was first described as one of the earth gods guarding the "gate to the yonder site". He protected the deceased king against the three demonic snakes Hemtet, Iqeru and Jagw. By "encircling" (i.e. interring) the deceased king, Aker sealed the deceased away from the poisonous breath of the snake demons. Another earth deity, who joined and promoted Aker's work, was Geb. Thus, Aker was connected with Geb. In other spells and prayers, Aker is connected with Seth and even determined with the Set animal. This is interesting, because Seth is described as a wind deity, not as an earth deity.

In the famous Coffin Texts of Middle Kingdom period, Aker replaces the god Kherty, becoming now the "ferryman of Ra in his nocturnal bark". Aker protects the sun god during his nocturnal travelling through the underworld caverns. In the famous Book of the Dead, Aker also "gives birth" to the god Khepri, the young, rising sun in shape of a scarab beetle, after Aker has carried Khepri's sarcophagus safely through the underworld caverns. In other underworld scenes, Aker carries the nocturnal bark of Ra. During his journey, in which Aker is asked to hide the body of the dead Osiris beneath his womb, Aker is protected by the god Geb.

In several inscriptions, wall paintings and reliefs, Aker was connected to the horizon of the North and the West, forming a mythological bridge between the two horizons with his body. Certain sarcophagus texts from the tombs of Ramesses IV, Djedkhonsuiusankh and Pediamenopet describe how the sun god Ra travels through the underworld "like Apophis going through the belly of Aker after Apophis was cut by Seth". In this case, Aker seems to be some kind of representation of the underworld itself.

Aker appears for the first time during the 1st Dynasty with the kings (pharaohs) Hor Aha and Djer. An unfinished decorative palette from the tomb of Djer at Abydos shows Aker devouring three hearts. The location of Aker's main cult center is unknown, though. His mythological role was fully described for the first time in the famous Pyramid Texts of king Teti.