What type of duty must an agent not act adversely to the principal's interests refer to?

The type of duty that requires an agent not to act adversely to the principal's interests is known as a fiduciary duty. A fiduciary duty is a legal obligation of one party to act in the best interest of another. In the context of an agency relationship, this means that the agent must prioritize the interests of the principal above their own, acting with loyalty and care to protect the principal's interests.

This duty encompasses various responsibilities, including avoiding conflicts of interest, not self-dealing, and providing full disclosure of relevant information related to the agency. The essence of fiduciary duty is the trust and confidence that the principal places in the agent, expecting them to act in a manner that benefits the principal.

In contrast, while a contractual duty relates to obligations specified by a contract and a legal duty refers to obligations imposed by law, neither fully captures the nature of the relationship inherent in agency. Personal duty is more ambiguous and does not convey the same level of obligation to act in someone else's best interest as fiduciary duty does. Thus, fiduciary duty is the most accurate term to describe the agent's responsibility to not act adversely to the principal's interests.