The professional educator or `sophist' was a prominent figure in Greek life from about 450 B.C. onwards. He was normally an itinerant lecturer who moved from city to city giving for fees instruction in accomplishments which it behoved an educated and ambitious Greek gentleman to possess, such as the art of persuasive speech, literature, and conventional morality. The class included many famous men, such as Protagoras and Gorgias, who could command large sums and a great following. Socrates, though he professed to teach nothing and accepted no fees, was frequently confused with the Sophists in the popular mind. Plato is at great pains to correct this misunderstanding, and constantly stresses the contrast between the philosopher, whose object is truth and virtue, and the sophist, who aims merely at making his pupils successful in life, and who may be totally sceptical. The dialogue Protagoras contains satirical portraits of a number of sophists, including Prodicus of Ceos, and the attack on them is pressed with much more vehemence and bitterness in the Gorgias and the first book of the Republic.