Nobody is ever born good or evil; villains are made, this is common knowledge. It's no different in Equestria, where we've seen the origin stories of nearly every great terror that has risen to threaten the peace and happiness of the land.
But no one seems to know much of the Lord of Chaos himself, Discord, before he ruled Equestria for his own personal enjoyment. However, like all villains, he did have his own life before seizing power, and this is where we discover his beginning and all that has happened since.
Cover art is by me