Oedipus: The king of Thebes. Prior to the beginning of the play, Oedipus was to be abandoned on a mountain, only a baby at the time, due to a prophesy that he would kill his father and wed and father children to his mother. He was instead given away, and his path led him elsewhere. However, he ended up killing his father after almost being killed by him, and then he went to Thebes, where he married his mother and fathered two daughters by her. He is unaware of all this, of course, and tries to find Laius' murderer so that Thebes will be free of the plague. When he finds out that it was he, he exiles himself.
Jocasta: The queen of Thebes, wife and mother to Oedipus. When she finds out who he is, that the prophesy came true, she kills herself.
Laius: The former king of Thebes, father and victim of Oedipus. He nearly ran him over with a carriage (on purpose) so it served him right. However, his death began the completion of a prophesy that his son would kill him and marry his mother.
Creon: Jocasta's brother. He shares power with Oedipus and Jocasta, and is a dear friend to them both. When Oedipus is exiled and Jocasta is dead, he takes over as king.