Aristotle of Stagira was a Greek philosopher who pioneered systematic, scientific examination in literally every area of human knowledge and was known, in his time, as "the man who knew everything", and, later, as "The Philosopher" (so named by Aquinas who felt one needed no other). In the European Middle Ages he is referred to as "The Master" in Dante's Inferno. All of these epithets are apt in that Aristotle wrote on, and was considered a master in, disciplines as diverse as biology, politics, metaphysics, agriculture, literature, botany, medicine, mathematics, physics, ethics, logic, and the theatre. He is traditionally linked in sequence with Socrates and Plato in the triad of the three greatest Greek philosophers.
Aristotle was born in 384 BCE in Stagira, Greece, on the border of Macedonia. His father, Nichomachus, was the court physician to the Macedonian king and died when Aristotle was ten years old. His uncle assumed guardianship of the boy and, as a teenager, Aristotle was sent to Athens to study at Plato's Academy where he remained for the next 20 years. He was an exceptional student, graduated early, and was awarded a position on the faculty teaching rhetoric and dialogue. It appears that Aristotle thought he would take over the Academy after Plato's death and, when that position was given to Plato's nephew Speusippus, Aristotle left Athens to conduct experiments and study on his own in the islands of the Greek Archipelago.
In 343 BCE Aristotle was summoned by King Philip II of Macedonia to tutor his son Alexander (who, of course, would become Alexander the Great) and held this post for the next seven years, until Alexander ascended to the throne and began his famous conquests. The two men remained in contact through letters, and Aristotle's influence on the conqueror can be seen in the latter's skillful and diplomatic handling of difficult political problems throughout his career. Alexander's habit of carrying books with him on campaign and his wide reading have been attributed to Aristotle's influence as has Alexander's appreciation for art and culture.
Aristotle returned to Athens to set up his own school, The Lyceum, a rival to Plato's Academy. Aristotle was a Teleologist, an individual who believes in `end causes' and final purposes in life, and believed these `final purposes' could be ascertained from observation of the known world. Plato, who also dealt with final causes, considered them more idealistically and believed they could be known through apprehension of a higher, invisible, plane of truth he called the `Realm of Forms'. Aristotle could never accept Plato's Theory of Forms nor did he believe in positing the unseen as an explanation for the observable world when one could work from what one could see backward toward a First Cause. While Plato claimed that intellectual concepts of the Truth could not be gained from experience, Aristotle claimed that they could be and taught these precepts to his students at the Lyceum. Aristotle's habit of walking back and forth as he taught earned the Lyceum the name of the Peripatetic School (from the Greek word for walking around, peripatetikos). His favorite student at the school was Theophrastus who would succeed Aristotle as leader of the Lyceum.
After the death of Alexander the Great in 323 BCE, when the tide of Athenian popular opinion turned against Macedon, Aristotle was charged with impiety owing to his earlier association with Alexander and the Macedonian Court. With the unjust execution of Socrates in mind, Aristotle chose to flee Athens, "lest the Athenians sin twice against philosophy", as he said, and died a year later in 322 BCE.
Aristotle's writings, like Plato's, have influenced virtually every avenue of human knowledge pursued in the west and the east. His Nichomachean Ethics (written for his son, Nichomachus, as a guide to good living) is still consulted as a philosophical touchstone in the study of ethics. He created the field and the study of what is known as `metaphysics', wrote extensively on natural science and politics, and his Poetics remains a classic of literary criticism.