Socrates The major speaker in the dialogue. His name means "master of life," and it is he who advances all of Plato's theories. Note that the Socrates who speaks in Plato's Dialogues is not, of course, the man, Socrates. The Socrates of the Dialogues serves as a persona (a mask, or fictive character) for Plato himself, who hoped, perhaps, thus to grant a kind of immortality to his teacher.
Cephalus A wealthy and retired old businessman, head of a business family. Socrates has known him a long time and admires him. Cephalus and Socrates initiate the dialogue, which begins with a casual friendly conversation. Cephalus' significance in the dialogue is that he exemplifies the seasoned experienced man who, though not a philosopher, has tried to live the good life and to adopt the virtues he has heard about. His remarks to Socrates at the beginning of the dialogue foreshadow topics that Socrates will develop later in the dialogue.
Polemarchus Cephalus' son and the pupil of Lysias, a teacher of rhetoric. It is Polemarchus (whose name means "war-lord" or "general") who instigates the flyting with Socrates during the festivities for the goddess Bendis before the dialogue proper begins. Polemarchus, perhaps true to his name, is very laconic in the dialogue, and he seems impatient with his "role" in it, seems resigned to his having "inherited" the responsibilities of host after Cephalus quits the conversation.
Thrasymachus A sophist, a teacher of specious rhetoric. His name means "rash fighter." Socrates seems particularly eager to engage Thrasymachus' arguments in the dialogue, and the two nearly reduce a philosophical dialogue to a petty quarrel.
Adeimantus An older half-brother of Plato. His name means "sooth-singer," and in the dialogue, he is a young man and something of a poet.
Glaucon Also a half-brother of Plato. His name means "owl" or "gleaming eyes," and in the dialogue, he is a young man.