Is the masked man who nods his head to Bill and then later he is in the library supposed to be Ziegler? It seems like it would be him since Ziegler mentions that he was at the masked event and that character is featured the most prominently in the sequence outside of Red Cloak.
shareThe consensus is that the nodding man was indeed Ziegler.
shareAs has been stated, the consensus is that the masked man is Ziegler.
Though I've always found it a bit much, that Ziegler would instantly recognize a masked Bill as he steps into the room.
They were onto Bill thanks to his arrival in a taxi, yes, and they found the rental info in his coat pocket, yes, but how would this information get to Ziegler so quickly and why would it get to Ziegler so quickly (why specifically him)? Presumably it didn't. Wouldn't. So we're left to conclude that the only way Ziegler would know it was Bill was by simple observation.
Which seems virtually impossible.
Perhaps Ziegler is the Senior Warden or Junior Warden of whatever the organization is with Red Cloak as the master and they share info with each other behind the scenes.
shareThe nodder is not Ziegler.
The film is partly about social class. Bill is a wealthy doctor, a big fish walking the streets of New York, but he’s small fry at the Ziegler’s party. Similarly, Ziegler is small fry at the Illuminati orgy.
The guy nodding will be another power-level above Ziegler.
Nodder and Red Cloak will have given Ziegler his marching orders to deal with Bill. Zieg will have pleaded Bill’s case and convinced them all he needed was some reassurance that nobody died and a final scare to forget what he saw and go back to living with his Eyes Wide Shut.