Neoplatonist Greek philosopher, important both as an editor and as a biographer of the philosopher Plotinus and for his commentary on Aristotle's Categories, which set the stage for medieval developments of logic and the problem of universals. Boethius' Latin translation of the introduction (Isagoge) became a standard medieval textbook.

Porphyry's original Syrian name (meaning “king”) was hellenized at Athens by Cassius Longinus, his teacher of rhetoric (the new name signifying “imperial purple,” an allusion to “king”). Porphyry studied philosophy (263–268?) in Rome under Plotinus, who gently rescued him from a suicidal depression. In 301 he produced his most important work, Enneads, a systematized and edited collection of the works of Plotinus to which was prefixed a biography, unique for its reliability and informativeness.

Porphyry's voluminous writings extended to philosophy, religion, philology, and science and show scholarly care in citing authorities. Surviving fragments of his Against the Christians, which was condemned in 448 to be burned, marked him as a fierce critic of the new religion. He was also lecturer on Plotinus and tutor to the Syrian philosopher Iamblichus, wrote a life of the mathematician Pythagoras, and preserved precious fragments of earlier philosophy in his On Abstinence, a plea for vegetarianism. In medieval textbooks, the “Porphyrian Tree” illustrated his logical classification of substance.