Rumors say that Discord once ruled Equestria and kept balance throughout the land but one day became bored and sent the planet into total chaos. Legend has it that and used the Elements of Harmony to encase him in stone for eons. Of course, these rumors can't possibly correct... Right?
Discord is arrogant and overconfident, as he underestimated the ponies' ability to restore their friendship and wield the Elements of Harmony. Despite having a fondness for chaos, he can become easily annoyed if things don't go according to his plan. Discord states that he's never had a friend. He appears touched when Fluttershy declares herself to be his friend, and it is that glimpse of genuine friendship that causes him to undo the chaos he had caused. He states at the end of the episode that he will use his magic only for good from now on: "most of the time". Since then he has kept his chaotic tendency to a low, though is still more than willing to cause mischief.
After he betrays the ponies of Equestria and Tirek subsequently betrays him, he shows deep remorse for his actions and apologizes to Fluttershy and her friends upon realizing the true importance of friendship. When Twilight and the others forgive him and the ponies accept him in the end, Discord appears truly happy
Powers and Abilities
Discord is able to warp reality on a fundamental level, changing the physical properties of the world around him and altering natural laws almost beyond recognition. As his power is chaos, he does not seem to have an easily determinable limit to what he can alter, though he was shown to have a limited range when he attacked Ponyville, as he was unable to alter several places at once.
Discord is shown to be skilled in performing magic and manipulating the minds of other creatures and ponies, twisting their personality or behavior in any way that amuses him. In the case of Twilight and her friends, he does so by confronting them with a trial that makes them question themselves. However, he is not above resorting to twisting their minds directly, as shown with Fluttershy. He can also change his physical appearance and size with relative ease.
Discord has the natural ability to sense major disturbances in magic.
Despite his powers, Discord does have his weaknesses. The Elements of Harmony are shown to have more power than Discord, allowing their users to entrap him in stone. His mind-altering abilities can also be broken, as when Twilight Sparkle overcomes her brainwashing by remembering the trials that made her friendship with the mane six bloom, as well as a memory spell she uses on the other five to make them remember who they are. Also, despite his powers, Discord is physically vulnerable to illness: the Tatzlewurm makes him legitimately sick and weak when it sneezes on him.
It is worth noting that, despite the royal sisters resorting to the Elements to defeat Discord, Discord himself resorted to using the plunder seeds to defeat the royal sisters rather than his own powers. In addition, Princess Celestia displays that she does have the power to repel Discord's chaotic magic, as she states in Keep Calm and Flutter On to have put a spell on the Elements of Harmony which prevents them from being affected by his magic.