Who said "I've learned that the greatest enemy is often within."?

This quote is attributed to Batman (1989).

I've learned that the greatest enemy is often within. - Batman (1989)

"I've learned that the greatest enemy is often within."

Batman (1989) Philosophy

"It's not who I am underneath, but what I do that defines me."

"I am vengeance, I am the night, I am Batman."

"Criminals are a superstitious and cowardly lot."

"I have one rule."

"I've seen the worst humanity has to offer."

"Sometimes I wonder if the world is worth saving."

"Every choice shapes our destiny."

"Order is the foundation of a good life."