What part did barney northrup play in the westing game?

We know from the start that Barney Northrup is not a real person, but we don't find out who's impersonating him until nearly the end of the book. What we do know about him is he's a fast-talking real estate dude with a funky mustache and great lying ability.

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Barney Northrup is one of Sam Westing's alternate identities: Sam Westing, Sandy McSouthers, Barney Northrup, and Julian Eastman.