Critias by Plato Critias (/ˈkrɪtiəs/; Greek: Κριτίας, Kritias; c. 460 – 403 BC) was an ancient Athenian political figure and author. Born in Athens, Critias was the son of Callaeschrus and a first cousin of Plato's mother Perictione. He became a leading and violent member of the Thirty Tyrants. He also was an associate of Socrates, a fact that did not endear Socrates to the Athenian public.

Critias was noted in his day for his tragedies, elegies, and prose works. Sextus Empiricus attributed the Sisyphus fragment to Critias; others, however, attribute it to Euripides. His only known play is Peirithous. In addition, eight shorter quotations from unidentified plays have come down to us.

Critias gave an account of his ancestry which was later recorded in Plato's Timaeus. Critias's great-grandfather, Dropidas, was an intimate friend of Solon. Dropidas's son, also named Critias, was the grandfather and namesake of the author Critias.

Critias was once a student of Socrates. The two had a strained relationship. However, it is said that Critias was the one who saved Socrates from persecution during the terror of the Thirty Tyrants. However, Critias was very greedy, something that Socrates did not approve of.

After the fall of Athens to the Spartans, Critias, as one of the Thirty Tyrants, blacklisted many of its citizens. Most of his prisoners were executed and their wealth confiscated.