(For other meanings of Porphyr, see Porphyry)

Porphyry (c. 232 AD - c. 304) was born Malchus ("king") in either Tyre or Batanaea in Syria, but his teacher in Athens, Cassius Longinus, gave him the name Porphyrius (clad in purple), a jesting allusion to the color of the imperial robes. Under Longinus he studied grammar and rhetoric. In 262 he went to Rome, attracted by the reputation of Plotinus, and for six years devoted himself to the study of Neoplatonism. Having injured his health by overwork, he went to live in Sicily for five years. On his return to Rome, he lectured on philosophy and endeavoured to render the obscure doctrines of Plotinus (who had died in the meantime) intelligible to the ordinary understanding. His most distinguished pupil was lamblichus, who differed with Porphyry on the issue of theurgy. In his later years, he married Marcella, a widow with seven children and an enthusiastic student of philosophy. Little more is known of his life, and the date of his death is uncertain.

Porphyry is best known for his contributions to philosophy. Apart from writing the "Aids to the Study of the Intelligibles," a basic summary of Neoplatonism, he is especially appreciated for his "Introduction to Categories" ("Introductio in Praedicamenta"), a commentary on Aristotle's Categories. The Introduction describes how qualities attributed to things may be classified, breaking down the philosophical concept of substance as a relationship genus - species.

As Porphyry's most influential contribution to philosophy, the Introduction to Categories incorporated Aristotle's logic into Neoplatonism, in particular the doctrine of the categories interpreted in terms of entities (in later philosophy, "universal"). Boethius' "Isagoge," a Latin translation of the Introduction, became a standard medieval textbook in the schools and universities which set the stage for medieval philosophical-theological developments of logic and the problem of universals. In medieval textbooks, the all-important Arbor porphyriana ("Porphyrian Tree") illustrates his logical classification of substance. To this day, taxonomists benefit from Porphyry's Tree in classifying everything from plants to animals to insects to whales.

Porphyry is also known as a violent opponent of Christianity and defender of Paganism; of his Adversus Christianas ("Against the Christians") in 15 books, only fragments remain. In this work. Counter-treatises were written by Eusebius of Caesarea, Apollinarius (or Apollinaris) of Laodicea, Methodius of Olympus, and Macarius of Magnesia, but all these are lost. Porphyry's identification of the Book of Daniel as the work of a writer in the time of Antiochus Epiphanes is given by Jerome. There is no proof of the assertion of Socrates, the ecclesiastical historian, and Augustine that Porphyry was once a Christian.

Porphyry also wrote widely on astrology (what would be considered astronomy in our day), religion, philosophy, and musical theory; and produced a biography of his teacher, Plotinus. Another book of his on the life of Pythagoras, named Vita Pythagorae or Life of Pythagoras, is not to be confused with the book of the same name by Iamblichus.