The character of Cratylus in the Cratylus is puzzling. Initially he is portrayed as a teasingly mysterious figure, and he is silent for most of it. But he adopts a quite different demeanour when he joins the conversation towards its end. Now he functions as a mostly reasonable and altogether cooperative respondent, even if he takes rigid and extreme positions. I argue that Plato uses Cratylus first to sketch linguistic naturalism in the dogmatic and dialectically unelaborated form in which it was presented by its original author. Then after Socrates has made of it a full scale philosophical theory on his own account, he puts Cratylus to another use: as a proponent of a version of that original naturalist position which is now developed as the germ of a rival full-scale theory in miniature, incorporating semantic, epistemological, and ontological components, and constructed from paradoxical stances generated by a range of previous and contemporary philosophers, including notably Antisthenes: a construction of Plato’s own. Hence for Plato Cratylus’ fascination: in the end his strange doctrine forces engagement with an interconnected set of deeply serious philosophical issues.