Heraclitus

either if you do it on purpose, as Heraclitus, 'surnamed the Obscure, because he wrote of nature too darkly,' or when the obscurity of the matter, not of the words, makes the discourse not understood, as is the case in Plato's Timaeus.

For he too, having learned from the barbarian philosophy, knows of the purification by fire of those who have lived ill — which the Stoics afterwards called conflagration;

and Heraclitus, still more nobly, that he himself discovered the nature of the universe, of what sort it is, with no one teaching him, and became wise from himself.

That Heraclitus, famous for dark speech

We all work together toward one accomplishment, some knowingly and with understanding, others without knowing it — just as Heraclitus, I think, says that even those who sleep are workers and fellow-labourers in what comes to pass in the universe.

Therefore Heraclitus, whose surname came from the obscurity of his speech, said:

For what that dark Heraclitus said — "the same way up and down.