Long ago, in the Magical Land of Equestria, there was a creature born of chaos and disharmony. A freak of nature, created only as a cruel joke of nature. The lonely being sought companionship, but was always denied it, thought to be a monster, a curse, a blight upon the beauty of Equestria. It prayed for happiness, and it came in the most unexpected of ways. A propechy was soon foretold; The End of Equestria, the end of the paradise of the ponies. The creature had grown in strength, and power as well. It heard of this prophecy, which said that four figures, representing negative powers in the perfect, utmost unholy Harmony, would unite their powers, and destroy the world. The prophecy would come true in a thousand years, when Twilight fell upon the five sparkling stars. The creature was born without a name, but it chose the name Discord, for it reigned over chaos.
It's power grew over the years, from conquering a small village, to laying waste to countrysides and striking fear into the heart of an entire nation. All were powerless to stop Discord's disharmonious chaos. The Alicorns worked tirelessly to form a solution to the evil that had risen from seemingly nowhere. They found five powerful gems, the most powerful, flawless, perfect magical gems in all the land, and gave them to the legendary Starswirl the Bearded, a stallion whose magical prowess was unrivaled through neither time or distance. It would take a total of five years to complete the magical gems, but he was certain he could craft them into powerful, harmonious tools of magic, capable of returning Harmony to the land, and, of course, stopping Discord.
Meanwhile, Discord knew that a thousand years would last longer than he had time to wait. He heard the whispers of the ponies plotting. A thousand years was too long to wait for the other three "figures" to reveal themselves, and far too long for the Alicorns and Ponies to prepare to destroy him. Without haste, Discord began his search for his prophesized allies, the Horsemen of the Apocalypse. Discord infiltrated the sanctum of the Crystal Ponies, and sought their ruler, King Sombra. He was hesitant to joining the creature, even to the promise of unlimited strength and ruling all of Equestria. Discord did not care for hesitance, and corrupted his mind to his will, creating the Horseman of Conquest. Discord, having dubbed himself the Horseman of Death instructed King Sombra to enslave his people, to create resources for an army.
While Sombra worked to gather resources for a future army, Discord saw jealousy in the highest of royalty. Princess Luna, the Alicorn responsible for raising the Moon at her older sister's side, grew tireless. Her sister's subjects deemed the night frightening, and meant for sleeping through. Discord infiltrated the Alicorn Capital and corrupted Luna in the middle of the night, transforming her into a wicked mare of darkness; Nightmare Moon, the Horsemare of War. She would be the mighty General that would guide and lead the mighty army that would destroy Equestria.
Discord instructed Nightmare Moon to find the final Horseman or Horsemare, and that he or she must be an alicorn. Nightmare Moon discovered a young, banished alicorn named Charm, who had fled to the Badlands from the wrath of Princess Celestia for her obsession over personal beauty, and attempting to steal a colt from his mate by corrupting his love. Out of options, Charm took Nightmare Moon's offer to become unimaginably beautiful, but at a cost. She was cursed by the corrupt alicorn to become a hideous creature, the first Changeling; To be forced to feed off of the love of other ponies; To have her visage warped in her own eyes, to appear beautiful in her own eyes, not the hideous creature she now was. The Alicorn, Queen Chrysalis, the new Horsemare of Famine, would create an army of changelings to destroy Equestria. King Sombra would provide armor, food, weapons, and et cetera for said army. And when the time came, Nightmare Moon would lead the army on a campaign of destruction, untill the shining kingdom of Equestria were nothing but a tarnished memory, crushed beneath the power of the Four Horsemen of the Apocalypse.
Five years had passed, and the powerful tools of magic were completed. Starswirl the Bearded soon after, having exhausted his body and soul, passed away. As his will had asked, his ashes were skattered to the winds of Canterlot by Pegasi. Before passing, Starswirl had told Princess Celestia that they could only be wielded by five ponies, or two alicorns. The Five Elements of Harmony, when used properly, would create the sixth element, Magic, and only Magic could harness the other five elements. Celestia was angry; Her sister was stolen from her by the fiend Discord, and she thought that her efforts were for nothing. In a last ditch effort, she confronted Nightmare Moon, and convinced her fragile, broken mind to turn upon her new allies. The two Alicorns used the new Elements of Harmony to seal Discord in stone, and banish King Sombra to the Arctic North, taking his cursed kingdom with him into the unknown. Finally, Celestia used the Elements of Harmony on Nightmare Moon; Unable to destroy her sister, she banished her to the moon. Chrysalis continued to create her army unbenownst to Celestia, awaiting the day that her allies would return.
For a thousand years, King Sombra wandered the Arctic Wastes of Equestria, a shell of his former self, barely able to think. For a thousand years, the Queen Chrysalis built an army of her children Changelings, ready to strike when she was commanded so. For a thousand years, Nightmare Moon waited patiently to be released from her lunar prison, quietly biding her time until the stars would aid in her escape.
And for a thousand years, Discord, Spirit of Disharmony and Chaos, plotted his revenge. The world had wronged him, and the world as a whole would pay dearly.