In the light of your understanding of tragedy and the tragic hero, how is Oedipus the King a tragedy?

One of the earliest and most influential of all
definitions of tragedy was proposed by the ancient Greek philosopher Aristotle in his
work known as The Poetics. Aristotle greatly admired Sophocles’
play Oedipus the King (Oedipus Rex), and
indeed he seems to have considered it the finest tragedy in existence. Certainly the
play exhibits a number of traits that Aristotle considered crucial to a successful
tragedy, including the following:

• The play
  exhibits a reversal of the sort Aristotle admired, as when he
  writes,

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Reversal of the Situation is a change by which
the action veers round to its opposite, subject always to our rule of probability or
necessity. Thus in the Oedipus, the messenger comes to cheer Oedipus and free him from
his alarms about his mother, but by revealing who he is, he produces the opposite
effect. (Butcher
translation)

• The
  play exhibits recognition, which Aristotle defines as “a change from ignorance to
  knowledge. He also writes that

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The best form of recognition is coincident with a
Reversal of the Situation, as in the
Oedipus.

• Aristotle
  thought that the best tragic figure would be “highly renowned and prosperous,” as
  Oedipus is initially.


• Aristotle thought that the tragic
  effects of pity and fear could be produced simply from hearing the plot of a tragedy, so
  that a tragedy’s success did not necessarily depend on being staged with spectacular
  means. He felt that hearing the plot alone of Sophocles’ Oedipus
  could produce pity and fear, thus indicating Sophocles’ skill as a
  dramatist.


• Aristotle felt that a good tragedy usually
  involved some “deed of horror” occurring between friends or between members of the same
  family, as in Oedipus.


• Aristotle
  felt that a tragedy should exclude the “irrational element,” either from its plot or
  from its presentation on stage. He thought that the latter exclusion occurred in
  Oedipus, particularly concerning Oedipus’s ignorance about the
  manner of Laius’s death.


• Aristotle believed that
  

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of all recognitions, the best is that which
arises from the incidents themselves, where the startling discovery is made by natural
means. Such is that in the Oedipus of
Sophocles.

• Aristotle
  commended Oedipus for being neither too long nor too short. He
  considered it exactly the right size to be an effective
  tragedy.

Above all, Aristotle believed that
Oedipus revealed all the key elements of an effective tragedy –
elements that Aristotle explained succinctly when he wrote
that

Tragedy
. . .is an imitation of an action that is serious, complete, and of a certain magnitude;
in language embellished with each kind of artistic ornament, the several kinds being
found in separate parts of the play; in the form of action, not of narrative; through
pity and fear effecting the proper purgation of these
emotions.

Aristotle's
definition of tragedy is perhaps the most influential that has ever been proposed.  In
formulating his definition, he seems to have had Sophocles' play in mind and to have
tested his definition at practically every point to make sure that Oedipus
Rex would be the perfect illustration of his theory.