Sophocles (496 BC-406 BC) was the second of the three greatest ancient Greek tragedians, the others being Aeschylus and Euripides. Of his 125 plays, only 7 survived. The story of Oedipus the King, or "Oedipus Rex" is part of a trilogy of tales whose most famous legacy is giving us the term "Oedipus complex", an unconsci0us desire for the parent of the opposite sex.
This triology of dramas describes the downfall of Oedipus as he struggles to avoid his fate. His father, Laius the king of Thebes, receives a prophecy that his newborn son will eventually kill him. To prevent this, he has his son taken into the wilderness to die. Instead, he is rescued and is adopted by the king of Corinth as his son. When Oedipus learns that he is prophesized to kill his father, he leaves Corinth to avoid this fate. This sends him on a collision course with his real father whom he meets and kills. He then unknowlingly marries his mother, the queen of Thebes, and they have several children.
(You know you have problems when you have a triangle in your family tree!)
When a plague strikes Thebes, the only cure is to discover and banish the man who killed Laius. Oedipus then learns through the oracle that he killed Laius, who was his father, and married his mother. In anguish, he blinds himself and then seeks refuge at Colonus, near Athens (Oedipus at Colonus) Oedipus's children then fight amoungst themselves as to who will succeed him as ruler, which raises the death count even higher. The last drama, Antigone, chronicles Oedipus's daughter Antigone as she struggles to have her brother buried near Thebes, which eventually leads to her own death as well.
I think that the theme of this story is that it is difficult to avoid fate. However, this entire tragedy could clearly have been averted if Oedipus had been ignorant of his lineage. Certainly ignorance would have been blissful compared to the chain of tragic events that unfolded after Oedipus discovered the consequences of his actions.
It was very insightful to read on the earliest and greatest tragedies that we have a record of. I can see where Shakespeare derived some of his inspiration, including the clever phrases and descriptions than Sophocles uses.