The protagonist in the play Oedipus Rex is the title character, Oedipus. Oedipus lives most of his life as a just man who seeks to avoid fulfilling the prophecy that he will kill his father and marry his mother. Indeed, when he learns of the prophecy, he decides not to return to the land where he believes his parents live in order to avoid doing them harm. The irony is that by leaving Corinth and returning to Thebes, he is returning to the place where his biological parents live; the parents he knew in Corinth were his stepparents.
The antagonist in this play is not a human character, or even a character as we have come to understand such in today's theater; instead, the antagonist is Fate itself. Fate, and the power of prophecy, drives all of the actions that are taken in the play--the fear of prophecy motivates Laius and Jocasta to abandon Oedipus as an infant and it motivates Oedipus to leave his adopted Corinth and return to Thebes, not know that by doing so, he is actually increasing the likelihood that he will fulfill the prophecy. Fate intervenes to persuade the shepherd charged with killing the boy Oedipus to spare his life, and Fate delivers the child to Corinth where he is raised in a royal family. Had Oedipus been raised a peasant, or a shepherd, it is unlikely that he would have gained the social station to marry a queen.
The primary theme running through the play is that of the role of fate in our lives. Laius and Jocasta seek to avoid fate by abandoning their child, Oedipus himself seeks to avoid fate by leaving the only home he has ever known, but none of these characters are able to escape their doom. Indeed, their actions seem to propel their destinies. One can argue that if Oedipus knew that Polybus and Merope were not his true parents, that Corinth was not the land of his birth, and that Corinth was the key to the prophecy, that he could have taken steps that would have helped him
...