Eternity

Eternity is a mysterious being who seems to be the living embodiment of the universe. Only three known beings—the Ancient One, Doctor Strange, and Dormammu—have spoken to Eternity. It lives in a dimension filled with symbols of the cosmos that are difficult for the human mind to parse. Eternity is blunt and intimidating, but apparently free of desire or emotion. When conversing, Eternity takes the form of a large, humanoid shape filled with a microcosm of celestial bodies.

In 1965, Doctor Strange entered Eternity's dimension with help from the Ancient One, seeking power with which to defeat the combined forces of Baron Mordo and Dormammu. Eternity refused, simply telling Strange that he didn't lack the necessary power, only the necessary wisdom. Strange was confused and distraught, having gone to great effort to receive an audience with Eternity, but he indeed went on to defeat Mordo and Dormammu, overcoming the power differential through his wits and strategy. Dormammu sought vengeance against Strange and fought him in Eternity's realm, casting a spell over Eternity in an attempt to keep it from interfering. Eternity broke through Dormammu's spell and confronted him. Eternity said that it would not have interfered normally, but Dormammu's attack had forced its hand. The bold and ambitious Dormammu was determined to destroy Eternity and become the foremost power in the universe, and he was prepared to die rather than bow to Eternity's power. The two collided in an enormous cataclysm as Strange watched from afar, dodging hurtling and exploding celestial bodies. Dormammu's body was destroyed—what became of Eternity is unclear.