Who is Major Frank Wirtanen from Mother Night and what is their importance?

Major Frank Wirtanen is a member of the U.S. War Department. He recruits the narrator to stay on in Germany after the war starts so that he can become an American spy. The narrator has no proof of his existence, and he simply contacts the narrator when it is most important. He often gets the narrator out of trouble. Even though the narrator only has contact with Wirtanen a few times in the book, he is a major character as Wirtanen serves as a mirror to the narrator. Wirtanen is always reminding the narrator that the life he has chosen is one of illusion. At one point, the narrator asks Wirtanen whether he trusts him.