Who are Simmias and Cebes?

These two individuals appear in the fourth and final dialogue, "Phaedo." Like Euthyphro in the dialogues that bear their names, Simmias and Cebes serve as the catalysts/vehicles for both Socrates' philosophical explorations and Plato's narration of those explorations. In terms of how their characters manifest, there is relatively little difference between them - Simmias is portrayed as being somewhat more confrontational and questioning, while Cebes is essentially in agreement with Socrates but has questions about one or two fine points of his (Socrates') philosophical arguments.