Diogenes Laërtius
Diogenes Laërtius was an ancient writer and historian of philosophy who presumably lived and worked in the 3rd century AD. Almost nothing is known about his own life — neither his exact year of birth nor his year of death can be determined with certainty. He may have come from Laerte in Cilicia (Asia Minor), as suggested by his epithet, though even this origin is not established.
The Principal Work: Vitae Philosophorum
His only surviving work, Vitae et sententiae philosophorum ("Lives and Opinions of Eminent Philosophers"), is one of the most significant source documents for the history of ancient philosophy. Across ten books, Diogenes portrays the lives and teachings of philosophers from a wide variety of schools — from the Pre-Socratics through Plato and Aristotle to the Stoics and Epicureans. In doing so, he compiled earlier sources, some of which are now lost, thus preserving invaluable information for posterity.
Significance for Stoic Philosophy
Diogenes Laërtius is particularly valuable as a source for the Stoa. In the seventh book of his work, he devotes extensive attention to the early Stoics: he describes the life and thought of Zeno of Citium, the founder of the Stoa, as well as his successors Cleanthes and, above all, Chrysippus of Soli. Regarding Chrysippus in particular — the "second founder" of the Stoa, who systematically elaborated the Stoic philosophical system — Diogenes transmits an extensive list of his writings as well as the core ideas of his philosophy in logic, physics, and ethics.
Without these records, our knowledge of the Early Stoa would be far more fragmentary, as the original writings of the early Stoics have been almost entirely lost. Diogenes thus serves as an indispensable intermediary between classical Stoic philosophy and modern scholarship.
Method and Style
Diogenes Laërtius did not work as a critically analytical historian in the modern sense, but rather as a collector and compiler. He drew from a wide variety of earlier sources, whose quality and reliability vary considerably. Anecdotes, biographical accounts, quotations, and doxographies stand side by side throughout his work. This often uncritical, yet all the more comprehensive approach renders his work both valuable and in need of careful interpretation.
Legacy
The Vitae Philosophorum were rediscovered during the Renaissance and had a lasting influence on the European image of the ancient philosophical schools. For research into the Stoa, Diogenes Laërtius remains to this day a primary source of the first order — a quiet custodian of the Stoic heritage in a world where papyrus and parchment succumbed to the passage of time.