First paper to introduce the "principal-agent problem" The principal-agent problem is to some extent an intuitive thing that even ancient kings must have thought about.

But what is the first journal paper that has introduced the term "principal" and "agent", and made the first formal economic analysis of the principal-agent problem as a general phenomenon?
The term principal-agent problem is due to Ross (1973) (per Stiglitz, 1989). Other early contributions to this literature include Mirrlees (1974, 1976) and Stiglitz 1974, 1975).