What was unusual about Barney Northrup in The Westing Game?

On the first page of The Westing Game the reader is alerted that Barney Northrup is not what he appears to be:

Then one day (it happened to be the Fourth of July), a most uncommon-looking delivery boy rode around town slipping letters under the doors of the chosen tenants-to-be.  The letters were signed Barney Northrup.
     The delivery booy was sixty-two years old, and there was no such person as Barney Northrup. (1)

Turtle finds out later that Barney Northrup, the somewhat shady real estate agent who gets all the heirs of Sam Westing's will to live together in Sunset Towers, is really one of the many disguises of the decidely not-dead Sam Westing.  All his aliases include a compass direction:

Why did Sam Westing have to play two roles, Turtle wondered.  He had a big enough part as the doorman without playing the real-estate man as well.  Why two roles?  No, not two, three.  Windy Windkloppel took three names; one: Samuel W. Westing, two: Barney Northrup, three: Sandy McSouthers. (170)

Sam Westing's other aliases melt away, of course, and he "dies" as Sandy McSouthers.  But he does not actually die, as Turtle finds out later; he lives out his days under his fourth alias: Julian Eastman.

Now she was on her way to meet the fourth identity of Windy Winkloppel.  She could probably have figured out the address, too, instead of looking it up in the Westingtown phone book -- there it was, number four Sunrise Lane.  ... Julian R. Eastman rose.... He was smiling.  He wasn't angry with her, he was smiling.
     "Hi Sandy," Turtle said.  "I won." (174-5)

The unusual thing about Barney Northrup is that he is really Sam Westing, a man who is supposed to be dead!  Barney wasn't real; he was a disguise invented by Sam to gather his heirs together to play the Westing Game.

Source: Raskin, Ellen.  The Westing Game.  New York: Avon Books, 1978.