Smallville, Season 2

Ryan:
Weren't they best friends?

Lex:
Once upon a time.

Ryan:
Well, what happened to them?

Lex:
Well, they ruled the Guardian Realm together until Devilicus told Warrior Angel that they should join forces and conquer humanity. Together, no one would be able to stop them.

Ryan:
What did Warrior Angel say?

Lex:
He refused. He believed it was a hero's sacred duty to protect those weaker than himself. Devilicus thought he was naive and vowed to destroy him and everything he stood for.

Ryan:
Why do you think Devilicus went bad?

Lex:
I'm not sure. Probably wasn't aware of it. You see, Ryan, in life, the road to darkness is a journey, not a light switch.

Ryan:
You should remember that, Lex.