Discord is one of the more powerful Ancient Ones in partnership to the Dark Lord Chernabog.
He is a minor antagonist in the Kingdom Hearts Unlimited Saga, first appearing in "The Keyblade Wars" as the primary boss of the Chaos Capitol campaign, but the impact he left on the worlds is all too important for the destinies of Palpatine, Maleficent, and Marwolaeth.
Discord was born long ago in the Age of Chaos as the spawn of Mother Chaos Prima and Father Chaos Prime, the divided incarnations of the original primordial void of madness and eldritch illogicies from which the multiverse itself sprang from. He, like his parents and siblings, Chaos Jr. and the three Eldritch Gods, started out as a formless yet intelligent mass of chaotic energy, but eventually he gained enough strength of will to forge for himself a physical body through which he could interact with the rest of his kind, the Ancient Old Ones.
For the first few millennia of his existence, Discord was merely content to cause harmless chaos in the fledgeling worlds of that era in the form of either a humanoid named Q or as a twisted hybrid beast known as a Draconequus. Then Chernabog happened. The Alpha Being of Darkness had gotten so envious of TOWIAA's power that he absorbed the full power of the original Void to become His equal as the first Satan, and began to gather like-minded beings with a thirst for destructive chaos to help him overthrow the Alpha Beings and bring an age of darkness upon the universe. Discord agreed to help out the rogue Alpha Being only out of sense of "he was so completely bored with his mundane existence", and was eventually rewarded by taking over the young world of Fourth Equestria as his cut of the prize. The son of Chaos itself thus ruled this world for millennia afterward, barely managing to avoid the same fate as his Ancient One bretheren by sheer dumb luck and staying long enough to see the rise of the Lands of Legend and the start of the the destructive Keyblade War.
Thinking he was safe from the depths of Tartarus by virtue of his lineage, Discord continued to rule Equestria as its god-king, but he was not a fool to be one day blindsided by his own defeat in the future. So, he began the implementation of back-up plans to be activated upon his eventual return: hiring apprentices to carry on his mad legacy, hiding several powerful artifacts across the worlds to be found one day by clueless sorcerers making a name for themselves, and making alliances with equally powerful beings in the hopes that they would aid him in his darkest hour. Soon enough, just after the X-Blade was sundered into 20 pieces on what would someday be known as the Keyblade Graveyard, Discord met his petrified end at the hands of the gods, and his stone statue hidden away in a secret cave on that fallen world. But never let it be said that Discord was gone forever, some say that it would only take a squabble or chaotic event to slightly chip away at the stone...and he would be free once more to rejoin his friends in making wonderful chaos again...