Stoicism

An ancient Greek philosophy founded in Athens around 300 BC by Zeno of Citium, built around the idea that virtue is the only true good and that external circumstances -- wealth, health, reputation -- are ultimately indifferent to a well-lived life. Stoicism shaped Roman emperors, early Christian theology, and Enlightenment thought. In the 21st century it staged a remarkable mainstream comeback, embraced by athletes, entrepreneurs, and self-help culture for its emphasis on resilience, emotional control, and focused action. Marcus Aurelius, Epictetus, and Seneca remain among the most widely read ancient philosophers today.

Added by @noahbennett