Steve Ditko: Strange Tales #146 (July, 1966)

Eternity was created as the second sentient force supporting Creation. Before Eternity, there was a single universe, whose animating force was the primal cosmic being that would later call itself The First Firmament. The First Firmament was attacked by its creations, The Celestials, during the catastrophic cosmic war that erupted between them and their counterpart creations, The Aspirants. The climax of that war resulted in the Celestials’ weapons tearing the first universe apart. The core essence of the First Firmament and the surviving Aspirants desperately fled to the void Outside creation. The torn fragments of the sundered first universe then coalesced into a new being that animated a new Reality that was made up of hundreds of universes. This Second Creation was the birth of the Multiverse and its animating force would later be called by the living entities within it Eternity. Creation would then evolve, die and be reborn six more times, each time evolving and changing to add new realities, forces and properties to itself-and all these changes would be reflected in the corresponding rebirth of Eternity. Therefore, after the destruction and rebirth of the Multiverse by the Beyonders, Eternity is in his 7th incarnation. (Wikipedia)