Cratylus is the name of a dialogue by Plato. Most modern scholars agree that it was written mostly during Plato's so-called middle period. In the dialogue, Socrates is asked by two men, Cratylus and Hermogenes, to tell them whether names are "conventional" or "natural", that is, whether language is a system of arbitrary signs or whether words have an intrinsic relation to the things they signify.
The individual Cratylus was the first intellectual influence on Plato (Sedley). Aristotle states that Cratylus influenced Plato by introducing to him the teachings of Heraclitus, according to MW. Riley.