Diogenes Laërtius (/daɪˈɒdʒɪniːz leɪˈɜːrʃiəs/; Greek: Διογένης Λαέρτιος, Diogenēs Laertios; fl. 3rd century AD) was a biographer of the Greek philosophers. Nothing is definitively known about his life, but his surviving Lives and Opinions of Eminent Philosophers is a principal source for the history of Greek philosophy. "Diogenes has acquired an importance out of all proportion to his merits because the loss of many primary sources and of the earlier secondary compilations has accidentally left him the chief continuous source for the history of Greek philosophy."
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