The Stranger has a very specific role in Oedipus in Colonus: explain to Oedipus that he’s in Colonus. Really, that’s it. He’s the guy who Antigone stops to ask for directions, and who tells them, oh, by the way, you’re in the place where it was prophesied you’d die. Have a nice day.
Um…yeah, nice to meet you too. At least the locals are nice.