Sam Westing was born with the name Windy Windkloppel. He changed it, presumably, to further his career as a paper tycoon. That accounts for two of his names; during the Westing Game Sam assumes three other identities, all in order to move the game along and give him access to the heirs during the game. The other identities are Sandy McSouthers, the (fake) Scottish doorman of Sunset Towers, Barney Northrup, the slightly shady real estate agent who leases the the apartments in Sunset Towers to the heirs, and the final alias, under which Sam Westing lives out his days as a distinguished retired man of business, Julian Eastman.
Since Sam began his days with a name like Windy, it stands to reason that he chose his points-of-the-compass aliases as a nod to his "windy" past. His four other names -- like the four winds -- all contain cardinal directions. Turtle Wexler eventually figures this out, and is shocked that she hadn't seen it before. She had been friends with Sandy, for example, for several weeks without once making the connection. Once the secret of the compass-points names was out, it was easy to figure out who everyone was. But Turtle kept Sam's (now Julian's) secret, and never told the other heirs.
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