A relationship between two parties in which one party (the agent) agrees to represent or act for the other (the principal).
Agency
As a noun, a person having a duty created by his or her undertaking to act primarily for another's benefit in matters connected with the undertaking. As an adjective, a relationship founded on trust and confidence.
Fudiciary
One who works for, and receives payment from, an employer but whose working conditions and methods are not controlled by the employer. An ____ is not an employee but may be an agent.