Diogenes likely washed up in Athens in the mid-360s, around the same time as a teenage Aristotle. At this point, Plato was nearly 60 and Antisthenes around 80—if, indeed, he was still alive.

Diogenes the Cynic (c. 412–323 BCE) was a contemporary of Plato, who once called him "a Socrates gone mad." After being exiled from his native Sinope for having defaced its coinage, Diogenes ...