Sophocles is considered one of the great ancient Greek tragedians. Among Sophocles' most famous plays are Oedipus the King, Oedipus at Colonus, and Antigone. These plays follow the fall of the great king, Oedipus, and later the tragedies that his children suffer. The Oedipus plays have had a wide-reaching influence and are particularly notable for inspiring Sigmund Freud’s theory of the "Oedipus Complex," which describes a stage of psychological development in which a child sees their father as an adversarial competitor for his or her mother’s attention (or in non-psychology speak, it’s the kill-the-father-sleep-with-the-mother complex).
The three plays are often called a trilogy, but this is technically incorrect. They weren't written to be performed together. In fact they weren't even written in order. Antigone, which comes last chronologically, was the play Sophocles wrote first, around 440 B.C. It wasn't until about 430 B.C that Sophocles produced his masterpiece Oedipus the King. He finally wrote Oedipus at Colonus in 401 B.C., near the end of his life. Also note that the plays were rarely if ever revived during the playwright's life time, so it's not like it would have been easy for Sophocles' audiences to compare them.
These facts probably explain some of discrepancies found in the plays. For example, while Creon is the undisputed King at the end of Oedipus the King, in Oedipus at Colonus it’s Polyneices and Eteocles who are battling for the throne. In Antigone, Creon assumes the throne with no mention of the fact that he's ever sat on it before. It's pretty unlikely that Sophocles forgot this key fact. But it could very well be that it just didn't matter very much. Each play is a separate interpretation of the myth, not a part of a trilogy. Sophocles would've been under no obligation to make the plays coherent in every detail.
Of course, while the plays aren't technically a trilogy and do have discrepancies, they do share many similarities. Several of the key characters put in repeat appearances, including Oedipus, Creon, Teiresias, Ismene, and Antigone. Also, the plays have a lot of the same themes. The plays all deal in some way with the will of man vs. the will of the gods. Self-injury and suicide also plague the family until the end. It seems that Oedipus's family is never quite capable of escaping the pollution of his terrible mistakes.
Stop us if you've heard this one before: guy walks into a bar, meets Han Solo, almost macks on his sister, steps up to save a galaxy, and finds out by the end of the second movie that his greatest enemy is *gasp* his father! Well, it's a familiar tale, not just for all moviegoers post-1977 – but also for all theatergoers after, say, 429 B.C.
Take out that bit about Han Solo (and also, maybe the bar), and change sister to mother and you've got the bare bones of Sophocles's Oedipus the King: guy gets chosen as the One to battle evil (sadly, not a host of stormtroopers; Sophocles goes with a plague caused by the evil presence of a murderer in Thebes), macks on his mother, and finds out that he himself was his father's killer without even knowing it.
Our point is: it seems kind of bizarre to us now to believe absolutely in fate. But all of Sophocles's characters believe in it, to the point where the father of this truly dysfunctional family (King Laius) is willing to order his infant son (Oedipus) killed when a prophecy tells him that his son will be his murderer. And all of the father's efforts to prevent his own death don't work. Why? Because it's fate: these characters have no real control over their own lives. Just like it's fate that Luke meets Leia and then Darth Vader.
The neat thing about fate in both Oedipus the King and Star Wars works is that, really, these guys don't have any control over their own lives – because they're fictional. After all, what kind of character development would there be if Darth Vader was defeated without knowing he was Luke's father? Would Darth Vader ever have **spoiler alert** been redeemed at the end? The relationship has to come out, or else there'd be no narrative after the first movie.
Oedipus marries his mother by accident, and if they were allowed to just hang around staying married and living in blissful ignorance, what would Sophocles be telling his audience? Nothing anyone would want to hear outside of Jerry Springer. So fate comes in to make sure we learn a lesson: marrying your mother and killing your father is so wrong that it will bring plague to your city and make you tear your own eyes out in horror. And in a way, maybe all fiction is about fate, even today: after all, fictional characters can’t avoid what their authors lay out for them.