 Protagoras (490–420 BCE ca) was one of the most important sophists and exerted considerable influence in fifth-century intellectual debates. His teaching had a practical and concrete goal, and many of the surviving testimonies and fragments suggest that it was mainly devoted to the development of argumentative techniques. But some of his views also raise important philosophical problems, which were going to be discussed in details by Plato, Aristotle, and many other philosophers. His famous thesis according to which “man is the measure of all things” has been interpreted as a first stance in favour of relativism, and his claim on the gods introduces the problem of agnosticism. Besides, his conventionalist notion of justice marks a break with the traditional account of divine justice; as it has been rightly claimed, it also seems to provide a theoretical foundation for democracy based on direct participation. By claiming a direct link with the great poets and thinkers of the past but also by appropriating and transforming their tenets, Protagoras presented himself as an heir to Greek paideia, as one of the great masters, or better, as the educator capable of imparting teachings suited to the needs of the new world of the polis.