Hellenistic Greek philosophers moderated and improved earlier philosophies into the ethical philosophy of Stoicism. The realistic, but morally idealistic philosophy was particularly popular among the Romans, where it was important enough to have been called a religion.
Originally, the Stoics were the followers of Zeno of Citium who taught in Athens. Such philosophers came to be known for the location of their school, the painted porch/colonnade or stoa poikile; whence, Stoic. For Stoics, virtue is all you need for happiness, although happiness is not the goal. Stoicism was a way of life. The goal of Stoicism was to avoid suffering by leading a life of apatheia (whence, apathy), which means objectivity, rather than not caring, and self control.
Marcus Aurelius was the last of the five so-called good emperors, which is fitting for a leader who tried to live virtuously. Marcus Aurelius is more familiar to many for his Stoic philosophical writing known as Meditations than his accomplishments as a Roman emperor. Ironically, this virtuous emperor was the father of a son known for his impropriety, Emperor Commodus.
None of the writing of the probably Phoenician Zeno of Citium (on Cyprus), the founder of Stoicism, remains, although quotations about him are contained in Book VII of Diogenes Laertius' Lives of Eminent Philosophers
. Followers of Zeno were at first called Zenonians.
Cleanthes was the second head of the Stoic school. He looked at physics as the base for ethics.
Chrysippus succeeded founder Cleanthes as head of the Stoic school of philosophy. He applied logic to Stoic positions, making them more sound.
Cato, the ethical statesman who vehemently opposed Julius Caesar, and was trusted for integrity, was a Stoic.
A Roman statesman and letter writer, Pliny the Younger admits that he is not Stoic enough to be merely content with the consciousness of having done his duty.
Epictetus was born a slave in Phrygia but came to Rome. Eventually he won his freedom from his crippling, abusive master and left Rome. As a stoic, Epictetus thought man should be concerned solely with will, which alone he can control. External events are beyond such control.
Lucius Annaeus Seneca (known as Seneca or Seneca the Younger) studied Stoic philosophy mixed with neo-Pythagoreanism. His philosophy is best known from his letters to Lucilius and his dialogues.