What is The Theme of Oedipus Rex?

Oedipus Rex is a Greek tragedy written by Sophocles, and it takes place in Thebes, Greece. The play begins with Thebes in the midst of a plague, and the king (Oedipus) is informed that he must find the murderer of his predecessor (Laius) to end the plague. Oedipus sends Creon to consult an oracle at Delphi to find out who the murderer is. The oracle tells Creon that Oedipus himself is the killer.
Oedipus is horrified and insists that he cannot be guilty because he was not born in Thebes; rather, he arrived there as an infant after being abandoned by his parents on Mount Cithaeron. He hires people to investigate this mystery and learns that Laius did indeed have children before him: Polybus and Merope, who raised Oedipus as their own son. In fact, Merope had given birth to twins—one of whom was not her husband’s child—and when Polybus found out about this indiscretion, he murdered his wife and then killed himself out of shame for what he had done to them both.