Critias (460-403 BC), son of Callaeschrus, was the uncle of Plato, leading member of the Thirty Tyrants, and one of the most violent. He was an associate of Socrates', a fact that did not endear Socrates to the Athenian public. He was noted in his day for his tragedies, elegies and prose works. From his Sisyphus a fragment has been preserved in which he declares faith in the gods to be merely a clever device for holding the masses in check; but as no one would dare to make such a statement before an Athenian audience, the piece was probably intended only for private reading — unless the quote was dialogue for the notoriously impious Sisyphus himself.
Critias appears as a character in Plato's dialogues Charmides and Protagoras. The Critias character in Plato's Timaeus and Critias is often identified as the son of Callaeschrus - but not by Plato; and given the old age of the Critias in these two dialogues, he must be the grandfather of the son of Callaeschrus.