Sophocles' "Oedipus the King" by At the outset of the play, Oedipus is the beloved ruler of the city of Thebes, whose citizens have been stricken by a plague. Consulting the Delphic oracle, Oedipus is told that the plague will cease only when the murderer of Queen Jocasta’s first husband, King Laius, has been found and punished for his deed. Oedipus resolves to find Laius’s killer. His investigation turns into an obsessive reconstruction of his own hidden past when he discovers that the old man he killed when he first approached Thebes as a youth was none other than Laius. At the end, Jocasta hangs herself in shame, and the guilt-stricken Oedipus blinds himself (britannica.com)
The story of Oedipus and the tragedies that befell his family were nothing new to Sophocles's audience. Greek authors routinely drew their basic material from a cycle of four epic poems, known as the Theban Cycle, that was already ancient in the fifth century B.C.E. and is now lost to history. The Theban Cycle was as familiar to Athenians as the The Iliad and The Odyssey, so everyone in the audience would have known what was going to happen to Oedipus. Sophocles used this common story but made Oedipus a contemporary character, a man of action and persistence who represented many of the ideals of Athenian leadership. It is Oedipus's desire to find out the truth—a quality that, again, would have been admired by Sophocles's audience—that leads to his destruction. (litcharts.com)
(496?–406 bc). The second of the three great Greek writers of tragic drama during the 5th century bc was Sophocles. Of the other two, Aeschylus preceded him, and Euripides was his successor. Sophocles is believed to have written 123 dramas, but only seven have survived. The best known is Oedipus Rex (or, Oedipus the King). The others are: Electra, Antigone, Trachinian Women, Ajax, Philoctetes, and Oedipus at Colonus. Fragments of lost plays and poems also exist. (Britannica Library)
The Three Theban Plays by 
