Arnold Zeck is a fictional character, the primary nemesis and "Moriarty" figure to detective Nero Wolfe in the mystery novels by Rex Stout. A sophisticated and dangerous criminal mastermind, Zeck runs a nationwide criminal syndicate and appears in three books—known as the "Zeck Trilogy"—where he clashes with Wolfe: And Be a Villain (1948), The Second Confession (1949), and In the Best Families (1950).