Based mostly on my fanart from deviantart . com; I simply HAD to write the story down. It was too good not to.
Despite the goodness of man, no matter how good, there is always the threat of evil inside. It's inevitable, unavoidable. Man can ignore it, suppress it, and minimalize it all they want, but it will always remain there; waiting, churning, and festering from disuse. All it takes is one wrong decision, one wrong choice, one wrong move, thought, or emotion for it to burst out, and that's when the bad things happen. That's when evil reigns supreme.
That's how villains are born. They are born from the outpour of suppressed evil that had been uncorked by a wrong decision, or festering emotions caused by an outside source. They turn to villainy to find an outlet for all of that evil inside of them, and very few manage to exhaust the evil and return to almost normal.
Some people, on the other hand, are born with evil. They live their lives as seemingly happy, good, and heroic people, and they are ultimately the worst of the ignorants, suppressors, and minimalizers; but in the end, they become the worst villains of all.
And this is the story of how a hero became a villain because of that evil which dwells in us all.