Porphyry (Greek: Πορφύριος, c. A.D. 233– c. 309) was a Neoplatonist philosopher. He is important in the history of mathematics because of his Life of Pythagoras, and his commentary on Euclid's Elements which was used by Pappus when he wrote his own commentary. 
Porphyry's parents were Syrian, and he was born Malchus ("king") in Tyre. His teacher in Athens, Cassius Longinus, gave him the name Porphyrius (clad in purple), a punning 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 returning to Rome, he lectured on philosophy and completed an edition of the writings of Plotinus (who had died in the meantime) together with a biography of his teacher. Iamblichus is mentioned in ancient Neoplatonic writings as his pupil, but this most likely means only that he was the dominant figure in the next generation of philosophers. The two men differed publicly 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 an opponent of Christianity and defender of Paganism; of his Adversus Christianos (Against the Christians) in 15 books, only fragments remain. He famously said, "The Gods have proclaimed Christ to have been most pious, but the Christians are a confused and vicious sect." 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 was also opposed to the theurgy of his disciple Iamblichus. Much of Iamblichus' mysteries is dedicated to the defense of mystic theurgic divine possession against the critiques of Porphyry.
Porphyry was, like Pythagoras, an advocate of vegetarianism on spiritual and ethical grounds. These two philosophers are perhaps the most famous vegetarians of classical antiquity. He wrote the De Abstinentia (On Abstinence) and also a De Non Necandis ad Epulandum Animantibus (roughly On the Impropriety of Killing Living Beings for Food) in support of abstinence from animal flesh, and is cited with approval in vegetarian literature up to the present day.
Porphyry also wrote widely on astrology, religion, philosophy, and musical theory. He produced a biography of his teacher, Plotinus. His book Vita Pythagorae on the life of Pythagoras is not to be confused with the book of the same name by Iamblichus.
Iamblichus: De mysteriis : Translated with an Introduction and Notes by Emma C. Clarke, John M. Dillon and Jackson P. Hershbell ISBN 90-04-12720-8
Dr. B.A. Zuiddam, Old Critics and Modern Theology. 1995; Dutch Reformed Theological Journal (South Africa), part xxxvi, number 2, June 1995.
Works by Porphyry
Ad Gaurum ed. K. Kalbfleisch. Abhandlungen der Preussischen Akadamie der Wissenschaft. phil.-hist. kl. (1895): 33-62.
Contra Christianos, ed., Adolf von Harnack, "Porphyrius, <<Gegen die Christen,>> 15 Bücher: Zeugnisse, Fragmente und Referate." Abhandlungen der königlich prüssischen Akademie der Wissenschaften: Jahrgang 1916: philosoph.-hist. Klasse: Nr. 1 (Berlin: 1916).
Contra los Cristianos: Recopilación de Fragmentos, Traducción, Introducción y Notas E. A. Ramos Jurado, J. Ritoré Ponce, A. Carmona Vázquez, I. Rodríguez Moreno, J. Ortolá Salas, J. M. Zamora Calvo (Cádiz: Servicio de Publicaciones de la Universidad de Cádiz 2006).
Corpus die Papiri Filosofici Greci e Latini III: Commentarii (Florence: Leo S. Olschki, 1995). <# 6 and #9 may or may not be by Porphyry>
De abstinentia ab esu animalium Jean Bouffartigue, M. Patillon, and Alain-Philippe Segonds, edd., 3 vols., Budé (Paris, 1979-1995).
De Philosophia ex oraculis haurienda G. Wolf, ed. (Berlin: 1956).
Epistula ad Anebonem, A. R. Sodano ed. (Naples: L'arte Tipografia, 1958).
Fragmenta Andrew Smith, ed. (Stvtgardiae et Lipsiae: B. G. Tevbneri, 1993).
The Homeric Questions: a Bilingual Edition Lang Classical Studies 2, R. R. Schlunk, trans. (Frankfurt-am-Main: Lang, 1993).
Isagoge, Stefan Weinstock, ed. in Catalogus Codicum astrologorum Graecorum, Franz Cumon, ed. (Brussels, 1940): V.4, 187-228.
Kommentar zur Harmonielehre des Ptolemaios Ingemar Duuring. ed. (Göteborg: Elanders, 1932).
Opuscula selecta Augusts Nauck, ed. (Lipsiae: B. G. Tevbneri, 1886).
Porphyrii in Platonis Timaeum commentarium fragmenta A. R. Sodano, ed. (Napoli: 1964).
Porphyry, the Philosopher, to Marcella: Text and Translation with Introduction and Notes Kathleen O’bBien Wicker, trans., Text and Translatiosn 28; Graeco-Roman Religion Series 10 (Atlanata: Schoalrs Press, 1987).
Pros Markevllan Griechiser Text, herausgegeben, übersetzt, eingeleitet und erklärt von W. Pötscher (Leiden: E. J. Brill, 1969).
Sententiae Ad Intelligibilia Ducentes E. Lamberz, ed. (Leipzig: Teubner, 1975).
Vie de Pythagore, Lettre à Marcella E. des Places, ed. and trans. (Paris: Les Belles Lettre, 1982).
La Vie de Plotin Luc Brisson, ed. Historie de l'antiquité classique 6 & 16 (Paris: Libraire Philosophique J. Vrin: 1986-1992) 2 vols.
Vita Plotini in Plotinus, Armstrong, ed. LCL (Cambridge, Mass.: Harvard University Press, 1968), 2-84.
To Marcella text and translation with Introduction and Notes by Kathleen O'Biren Wicker (Atlanta: Scholars Press, 1987).
The Cave of the Nymphs in the Odyssey A revised text with translation by Seminar Classics 609, State University of New York at Buffalo, Arethusa Monograph 1 (Buffalo: Dept. of Classics, State University of New York at Buffalo, 1969).
Isagoge Mediaeval Sources in Translation 16, E. Warren, trans. (Toronto: Pontifical Institute of Mediaeval Studies, 1975).
Isagoge, J. Tricot, trans. (Paris: J. Vrin, 1947).
Neoplatonic Saints: The Lives of Plotinus and Proclus Translated Texts for Historians 35 (Liverpool: Liverpool University Press, 2000).
On Abstinence from Killing Animals Gilliam Clark, trans. (Ithaca: Cornell University Press, 2000).
On Aristotle's Categories Steven K. Strange, trans. (Ithaca: Cornell University Press, 1992).
On the Cave of the Nymphs Robert Lamberton, trans. (Barrytown, N. Y.: Station Hill Press, 1983).
The Organon or Logical Treatises of Aristotle with the Introduction of Porphyry Bohn's Classical Library 11-12, Octavius Freire Owen, trans. (London: G. Bell, 1908-1910), 2 vols.
Porphyry Against the Christians, R. M. Berchman, trans., Ancient Mediterranean and Medieval Texts and Contexts 1 (Leiden: Brill, 2005).
Porphyry’s Against the Christians: The Literary Remains R. Joseph Hoffmann, trans. (Amherst: Prometheus Books, 1994).
Five Texts on the Mediaeval Problem of Universals: Porphyry, Boethius, Abelard, Duns Scotus, Ockham Paul Vincent Spade, trans. (Indianapolis: Hackett, 1994).