What is the background of Oedipus the king?
Oedipus, the king of Thebes at the beginning of the play, believes that he hails from Corinth and is the son of King Polybus and Queen Merope. However, he is really the son of King Laius and Queen Jocasta from Thebes. His birth parents heard a prophecy that their son would kill his father and marry his mother, and so they sent the baby Oedipus away with a servant to be killed in the woods. This servant instead gave him to another servant from house of Polybus. Thus, Polybus and Merope raised Oedipus as their own.
One day, when he's grown up, a drunken man tells him that he's been adopted, and so he goes to the oracle of Delphi to learn the truth. Instead of answering his questions, the oracle tells him the same prophecy Laius had heard: that he would kill his father and marry his mother. Oedipus decides, then, not to return home to Corinth so that he cannot fulfill the prophecy. On the road, he gets into an altercation and kills all but one man in the party, and it turns out that one of the men he killed was Laius, his birth father. Then, after he frees Thebes from the dreadful sphinx by answering her riddle, the Thebans make him the king and he marries the old king's wife, Jocasta, who is actually his mother. In this way, he has fulfilled the prophecy before the play has even begun.