Cratylus (/ˈkrætɪləs/ KRAT-il-əs; Ancient Greek: Κρατύλος, Kratylos) was an ancient Athenian philosopher from the mid-late 5th century BC, known mostly through his portrayal in Plato's dialogue Cratylus. He was a radical proponent of Heraclitean philosophy and influenced the young Plato.