Thrasymachus was a sophist and teacher of rhetoric from Chalcedon, active in Athens during the late 5th century BCE. He was part of the vibrant intellectual circle that included figures like Socrates and Gorgias. While the details of his life are sparse, ancient sources indicate he taught the art of persuasive speaking and composed speeches for both legal and display purposes. He is most famously portrayed as a character in Plato’s Republic, where he argues that justice is merely “the advantage of the stronger,” a provocative idea that Plato’s Socrates spends considerable effort refuting.

None of Thrasymachus’s own writings survive intact; we know of them only through fragments and descriptions by later authors. He is credited with writing handbooks on rhetorical technique and model display speeches. A portion of a speech called the Appeal to the Athenians survives, quoted by a later critic to illustrate Thrasymachus’s distinctive style.

His significance is twofold. In the history of rhetoric, he is recognized as an important stylistic innovator. According to ancient critics like Cicero, he helped develop a more rhythmic and emotionally powerful prose style. In political philosophy, his argument in the Republic presents a foundational challenge, forcing a defense of justice as something more than a tool for the powerful. Despite the loss of his original works, his ideas on power, persuasion, and morality have remained influential through the writings of his critics and commentators.