Epictetus (Greek: Επίκτητος; c.55–c.135) was a Greek Stoic philosopher. He was probably born at Hierapolis, Phrygia, and lived most of his life in Rome until his exile to Nicopolis in northwestern Greece, where he died. The name given by his parents, if one was given, is not known - the word epiktetos in Greek simply means "acquired."
Epictetus spent his youth as a slave in Rome to Epaphroditos, a very wealthy freedman of Nero. Even as a slave, Epictetus used his time productively, studying Stoic Philosophy under Musonius Rufus. He was eventually freed and lived a relatively hard life in ill health in Rome. It is known that he became crippled, yet the exact cause remains in dispute. Some reports claim that his injuries were a result of cruel treatment by his owner, Epaphroditos, while yet other reports claim that Epaphroditos was an ideal master who enthusiastically supported Epictetus' studies. He was exiled along with other philosophers by the emperor Domitian sometime between 89 and 95.
It was Epictetus' exile by Domitian that began what would later come to be the most celebrated part of his life. After his exile, Epictetus traveled to Nicopolis, Greece, where he founded a famed philosophical school. This school was even visited by Hadrian, and its most famous student, Arrian, became a great historian in his own right.
True to Stoic form, Epictetus lived a life of great simplicity, marked by teaching and intellectual pursuits. Some claim that he married once, late in life, to help raise a child who would have otherwise been left to die. Others say that he did not marry, and remained childless.
Demonax supposedly rebuked Epictetus' exhortation to marry by sarcastically asking whether he could marry one of the philosopher's daughters.
So far as is known, Epictetus himself wrote nothing. All that we have of his work was transcribed by his pupil Arrian (author of the Anabasis Alexandri).  The main work is The Discourses, four books of which have been preserved (out of an original eight). Arrian also compiled a popular digest, entitled the Enchiridion, or Handbook. In a preface to the Discourses, addressed to Lucius Gellius, Arrian states that "whatever I heard him say I used to write down, word for word, as best I could, endeavouring to preserve it as a memorial, for my own future use, of his way of thinking and the frankness of his speech".
Epictetus focused more on ethics than the early Stoics had. Repeatedly attributing his ideas to Socrates, he held that our aim was to be masters of our own lives. The role of the Stoic teacher, according to Epictetus, was to encourage his students to learn, first of all, the true nature of things, which is invariable, inviolable and valid for all human beings without exceptions. The ‘nature of things’ is their partition into two categories; those things that are subject to our exclusive power (prohairetic things) and those things that are not subject to our exclusive power (aprohairetic things). The first category of things includes judgment, impulse, desire, aversion, etc. The second category of things, which can also be called adiaphora, includes health, material wealth, fame, etc. Epictetus then introduced his students to two cardinal concepts: the concept of Prohairesis and the concept of Dihairesis. Prohairesis is what distinguishes humans from all other creatures. It is the faculty that makes us desire or avert, feel impelled or repel something, assent to or dissent about something, according to our own judgments. Epictetus repeatedly says that "we are our prohairesis". Dihairesis is the judgement that is performed by our Prohairesis, and that enables us to distinguish what is subject to our exclusive power from what is not subject to our exclusive power. Finally, Epictetus taught his students that good and evil exist only in our Prohairesis and never in external or aprohairetic things. The good student who had thoroughly grasped these concepts and employed them in everyday life was prepared to live the philosophic life, whose objective was eudaimonia (happiness or flourishing). This meant living virtuously, in accordance with reason and in accordance with the "nature of things".
The essence of Epictetus's psychology is revealed by two of his most frequently quoted statements:
We are disturbed not by events, but by the views which we take of them.
I must die. Must I then die lamenting? I must be put in chains. Must I then also lament? I must go into exile. Does any man then hinder me from going with smiles and cheerfulness and contentment?
In the last chapter in Enchiridion he concludes his ethics with four maxims meant to help during everyday life:
"Lead thou me on, O Zeus, and Destiny,
To that goal long ago to me assigned.
I'll follow and not falter; if my will
Prove weak and craven, still I'll follow on.
"Whoever has complied well with necessity
Is counted wise by us, and understands divine affairs. (From Euripides, Frag. 965)
"O Crito, if it thus pleases the gods, thus let it be." (From Plato's Crito)
"Anytus and Meletus can kill me, but they can't harm me." (From Plato's Apology)
The influence of Epictetus continues today. Psychologist Albert Ellis, the founder of Rational Emotive Behavior Therapy, credits Epictetus with providing a foundation for his system of psychotherapy (How to Refuse to Make Yourself Miserable about Anything, 1998). (In about 1995, a survey by the American Psychological Association ranked Ellis as the most influential psychologist in twentieth-century America, after Carl Rogers. Freud ranked third.)
James Stockdale was an American fighter pilot who was shot down over North Vietnam, and was later a vice presidential candidate. In Courage under Fire : Testing Epictetus's Doctrines in a Laboratory of Human Behavior (1993), Stockdale credits Epictetus with helping him endure seven and a half years in a North Vietnamese military prison – including torture, and four years years in solitary confinement. In his conclusion, Stockdale quoted Epictetus as saying, "The emotions of grief, pity, and even affection are well-known disturbers of the soul. Grief is the most offensive; Epictetus considered the suffering of grief an act of evil. It is a willful act, going against the will of God to have all men share happiness" (p. 235).
The philosophy of Epictetus plays a key role in the 1998 novel by Tom Wolfe, A Man in Full.