Socrates's distinctive method of finding truth through questions and answers is called the dialectic method. In the Republic it is Socrates who persuades the other characters to agree to certain crucial premises: for example, the parallel between justice in the ideal state and justice in the individual. From other sources, readers can glean various biographical facts about Socrates. For instance, he was striking for his physical ugliness. He was married to a quarrelsome wife named Xanthippe, and he served in the Athenian army as the equivalent of an infantryman.
Glaucon, who seems to have been at least 15 years older than Plato, is spirited, experienced, and articulate. At the beginning of Book 2, for example, Glaucon takes the initiative by telling the myth of Gyges in order to show people conform to justice only because they do not want to risk punishment for behaving unjustly. It is also to Glaucon Socrates offers his striking explanation of the Allegory of the Cave in Book 7.
Adeimantus is portrayed as more sober and pessimistic than his brother Glaucon. For example, at the beginning of Book 4 Adeimantus displays a pessimistic outlook when he complains Socrates seems to have prescribed a life of deprivation, even misery, for the guardians in the ideal state. Socrates goes to considerable lengths to refute this objection.
Thrasymachus champions a cynical view of justice, claiming it is nothing more or less than "the interest of the stronger." His position can be described as "might makes right." Although his contributions are largely limited to Book 1, Thrasymachus casts a long shadow over the dialogue since Socrates refutes his argument all the way through Book 9.