Definition & Meaning of "you either die a hero or live long enough to see yourself become the villain"in English

What is the origin of the proverb "you either die a hero or live long enough to see yourself become the villain" and when to use it?

The origin of the proverb "you either die a hero or live long enough to see yourself become the villain" is often associated with the 2008 film 'The Dark Knight.' In the movie, the character Harvey Dent starts as a heroic figure but eventually turns into the villain Two-Face as his ideals and sense of justice are corrupted. The saying implies that even the most virtuous individuals can be changed over time by circumstances, power, or moral compromise. It serves as a warning about how power, success, and challenges can lead people to abandon their principles and ultimately transform into what they once opposed.