Cupboard "Cup" Salt is a skilled infiltrator and a member of the Black Slacks. Along with Beau, Sige, and Aubrey, Cup helped rob an auction for the first book ever written.
Cup is a factory worker from Iris Parish. He's "slim, wears oversized clothes with too-long sleeves, a bright yellow shirt with purple stitching, and is kind of a slippery little shit." He can become ghostly and insubstantial. He looks slightly like Samot, enough that (with some styling before the heist) Samothes saw the resemblance.
At the end of the GenCon Liveshow, he attempted to make off with the book they were after, while Sige tried to stop him.