Critias

Critias is also a work by Plato, see Critias (dialogue). Critias (Greek , 460-403 BC), born in Athens, son of Callaeschrus, was the uncle of Plato, and a 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. Some, like  Sextus Empiricus, believe that Critias authored the Sisyphus fragment; others, however, attribute it to Euripides.
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