Creon is one of the main characters in "Oedipus Rex" by Sophocles. He is the younger brother of Laius, king of Thebes. This makes him the uncle of Oedipus, something we do not find out until after it is revealed towards the end of the play that Oedipus is actually the son of Laius and Jocasta.
At the opening of the play, Creon is one of the important advisers to Oedipus, and well respected in Thebes. Oedipus has sent him to the famed oracle of Apollo at Delphi to discover the source of the plague, and Creon reports that Apollo has sent the plague because Thebes is sheltering the murderer of Laius.
Oedipus thinks that Creon is plotting for the throne, although there is no evidence that such is the case. When Oedipus' parentage is revealed and Oedipus blinds himself, Creon does, in fact, assume the throne of Thebes.