Complex sentence: Born in Athens, Critias was the son of Callaeschrus and a first cousin of Plato's mother Perictione, and became a leading and violent member of the Thirty Tyrants.
Split into simpler sentences: 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.