Final answer:
A Guard is the one who reports to King Creon about the attempt to bury Polyneices' body, not Ismene, Eteocles, Haemon, or Antigone.
Step-by-step explanation:
The character who enters to announce to King Creon that someone has attempted to bury the body of Polyneices is none other than a Guard. It is not one of the main characters such as Ismene, Eteocles, Haemon, or Antigone. The Guard informs Creon of the act, which sets into motion the tragic events that unfold as Antigone is caught and ultimately faces her demise due to her defiance of Creon's edict.