A long time ago, before the world was created, there was Chaos. Chaos ruled the universe and from Chaos came Cronos. Cronos was lord of space and time, and made sure both space and time were as confusing as Chaos wished it to be. Chaos was corrupted by the power he wielded and turned evil, making the inhabitants of the universe suffer.
But for Chaos to exist, Order must also exist. And from Order came the goddess Gaia. Gaia was taught by Order to be gentle and kind, and so she became the goddess of love and earth. Order herself wished for the universe to be freed from the grasp of Chaos, at least partly, but would not fight. She instead sent her daughter out to care for the many worlds of the universe. However all the worlds in the universe were entirely corrupted by Chaos, and so Gaia set out to free them, one by one. Every world she visited she treated the inhabitants with grace and kindness, and taught them the way of Order. Slowly Chaos and Order began to balance each other out. Chaos saw this and was not happy. So he sent his son out to stop Gaia and return the worlds she had visited to Chaos.
Yet when Cronos met Gaia he saw in her a peace he had never felt before, and she saw in him a wildness she had never experienced. So the two fell in love and left their feuding parents behind. They fled to an obscure part of the universe and using Cronos's Chaos created Equestria. Gaia populated it with the ponies using her Order, and they watched over their creation for many years.
But Chaos had gained back all the power Gaia had stole from him by turning the worlds to Order, and was furiously searching for the two. When he found them he corrupted Equestria, which had been made using the powers his son had inherited from him. Seeing the danger their creation was in, Cronos and Gaia took mortal form in order to come down to Equestria. They fended off Chaos and united the ponies of Equestria. They ruled for many years and a Golden Age came over the land. It was during this time that they birthed their two children, Luna and Celestia. This is their tale.