Euthyphro: Presumably a middle-aged man and acquaintance of Socrates, who has just deposed murder charges against his father.  He seems a bit pompous as he claims to have esoteric knowledge of piety, and holds fast to his claim even though Socrates clearly refutes it.

Socrates: A seventy year old, short, snub-nosed philosopher on his way to answer charges against himself.  He is a kind-hearted and good-spirited fellow, eager to converse with nearly anyone, as he truly loves to learn.  He is keen and quick-witted, as Plato rightly presents him, and the central character in many of Plato's dialogues.