Greek Peripatetic philosopher and pupil of Aristotle. He studied at Athens under Aristotle, and when Aristotle was forced to retire in 323 he became the head of the Lyceum, the academy in Athens founded by Aristotle. Under Theophrastus the enrollment of pupils and auditors rose to its highest point.

Theophrastus was one of the few Peripatetics who fully embraced Aristotle's philosophy in all areas of metaphysics, physics, physiology, zoology, botany, ethics, politics, and history of culture. His general tendency was to strengthen the systematic unity of those subjects and to reduce the transcendental or Platonic elements of Aristotelianism as a whole. Of his few surviving works, the most important are Peri phytōn historia (“Inquiry into Plants”) and Peri phytōn aitiōn (“Growth of Plants”), comprising nine and six books, respectively. Of dubious origin are the smaller treatises attributed to him on fire, winds, signs of weather, scents, sensations, and other subjects. His notable Charaktēres (many English translations) consists of 30 brief and vigorous character sketches delineating moral types derived from studies that Aristotle had made for ethical and rhetorical purposes; this work later formed the basis for the masterpiece of Jean de La Bruyère, Les Caractères . . . (1699). In his ethical teachings, famous because of the assaults of the Stoic philosophers, Theophrastus reiterated Aristotle's notion of a plurality of virtues with their relative vices and acknowledged a certain importance to external goods, which the Stoics held were mere luxuries for human life.

Among Theophrastus' other works is the Physikōn doxai (“Opinions of Natural Philosophers”). As reconstructed by Herman Diels in Doxographi Graeci (1879), it provides a foundation for the history of ancient philosophy.