(Κριτόλαος), the Peripatetic philosopher, was a native of Phaselis, a Greek colony in Lycia, and studied philosophy at Athens under Ariston of Ceos, whom he succeeded as the head of the Peripatetic school. The great reputation which Critolaus enjoyed at Athens, as a philosopher, an orator, and a statesman, induced the Athenians to send him to Rome in B. C. 155, together with Carneades the Academic and Diogenes the Stoic, to obtain a remission of the fine of 500 talents which the Romans had imposed upon Athens for the destruction of Oropus. They were successful in the object for which they came; and the embassy excited the greatest interest at Rome. Not only the Roman youth, but the most illustrious men in the state, such as Scipio Africanus, Laelius, Furius, and others, came to listen to their discourses. The novelty of their doctrines seemed to the Romans of the old school to be fraught with such danger to the morals of the citizens, that Cato induced the senate to send them away from Rome as quickly as possible. (Plut. Cat. Ma. 22; Gel. 7.14; Macrob. Saturn. 1.5; Cic. de Orat. 2.37, 38.) We have no further information respecting the life of Critolaüs. He lived upwards of eighty-two years, but died before the arrival of L. Crassus at Athens, that is, before B. C. 111. (Lucian, Macrob. 20; Cic. de Orat. 1.11.)

Critolaus seems to have paid particular attention to Rhetoric, though he considered it, like Aristotle, not as an art, but rather as a matter of practice (τριβή). Cicero speaks in high terms of his eloquence. (Quint. Inst. 2.15.23, 17.15; Sext. Empir. ad v. Mathem. 2.12, p. 291; Cic. de Fin. 5.5.) Next to Rhetoric, Critolaüs seems to have given his chief attention to the study of moral philosophy, and to have made some additions to Aristotle's system (comp. Cic. Tusc. 5.17; Clem. Al. Strom. ii. p. 416), but upon the whole he deviated very little from the philosophy of the founder of the Peripatetic school. (Stahr, Aristotelia, ii. pp. 83, 135; Fabric. Bibl. Graec. ii. p. 483.)