Sophocles' Oedipus the King appears to have been the favorite play of the author of the Poetics, who, for argument's sake, we will refer to as Aristotle. We need to be precise, though, about what Aristotle is up to. Aristotle provides some brief remarks on what he thinks the character of the tragic hero should be like:
"There remains, then, the character between these two extremes,—that of a man who is not eminently good and just,-yet whose misfortune is brought about not by vice or depravity, but by some error or frailty. He must be one who is highly renowned and prosperous,—a personage like Oedipus, Thyestes, or other illustrious men of such families" (S. H. Butcher translation).
Aristotle does not go into detailed analysis of how the tragic hero will behave. Aristotle is, however, more interested in how the plot of the "perfect tragedy" (S. H. Butcher translation) should be constructed.
Regarding the tragic hero's character, Aristotle claims that the most effective type of tragic drama occurs when a famous person, who is neither incredibly virtuous or extremely wicked, goes from good fortune to bad fortune due to some "error or frailty" (S. H. Butcher translation).
This is, of course, exactly what happens in Oedipus the King, as Oedipus moves from being regarded as the savior of Thebes (he had solved the riddle of the Sphinx and thus ended that monster's reign of terror) to being considered the most horrific person in Thebes (by the end of the play he discovers that he has killed his father and had sexual relations with his mother).
In my view, Oedipus' downfall is not caused by pride or a bad temper (with which so many modern readers of the play seem to saddle Oedipus), but rather he had the horrific misfortune of being in the wrong place at the wrong time. Oedipus also had the perhaps even more horrific misfortune of coming to realize that what the gods said he would do in his lifetime did come to pass. Oedipus did, indeed, experience a "series of unfortunate events" resulted in him killing his father and marrying his mother.