Stoicism was a philosophy that flourished for some 400 years in Ancient Greece and Rome, gaining widespread support among all classes of society. It had one overwhelming and highly practical ambition: to teach people how to be calm and brave in the face of overwhelming anxiety and pain. There are several famous stoic philosophers including Marcus Aurelius and Epictetus. Nearly all religions have a foundation in stoic principles.
The Stoics sought what they called apatheia – the state of mind where one is free from emotional disturbance. It is a positive term referring to the act of nullifying emotional responses to things outside of our control. Apatheia is the best and most rational response to the world in which we accept that we cannot control things caused by the will of others or by Nature and that we can only control ourselves and our reactions to said external events. Apatheia does not encourage a loss of feeling or an indifference to emotions, but rather it seeks to bring you closer to clarity and rationality using logic, reflection, concentration, and mindfulness.
The Stoics believed that unhappiness and evil were the result of human ignorance to their own value within the universe and that the solution was to examine oneself fully and determine where your understanding of yourself veered off from the reality of your purpose. Anger, in Stoic philosophy, is caused by the violent collision of hope and reality.