Final answer:
Creon is the second-in-command in Thebes, brother-in-law of Oedipus, and a trusted advisor selected to seek Apollo's advice in saving the city from plague.
Step-by-step explanation:
The second-in-command in Thebes, brother-in-law of Oedipus, and a trusted advisor selected to go to the oracle at Delphi to seek Apollo's advice in saving the city from plague is Creon. In the play, Oedipus sends Creon to the oracle after a terrible plague hits Thebes and the oracle reveals that the plague will only be lifted if the killer of the previous king, Laius, is brought to justice. Creon plays a crucial role in the story as a loyal and trusted councilor to both Laius and Oedipus.