During the last two centuries, courts have been adapting this duty of loyalty and its remedy to other agency relations, under the title "fiduciary" duty.1 That is adaptation, not extension. The many agency relations that fall under the "fiduciary" banner are so diverse that a single rule could not cover all without wreaking havoc. Courts have applied the term to relations as diverse as guardian-ward, attorney-client, and bank-borrower. Does anything other than the word "fiduciary" and an appeal to a duty of loyalty (in its strong form, a duty that the agent work for the "exclusive benefit" of the principal) unite these situations? Principles of ethics? Is the fiduciary morally bound to act in a particular way, perhaps? Or are the different situations wholly distinct, so that a union's fiduciary "duty of fair representation" in labor law is unrelated to a corporate manager's fiduciary obligations to investors?