Final answer:
A person given legal authority to act on another's behalf through a power-of-attorney is known as an agent, with the individual granting the power being the principal.
Step-by-step explanation:
A person designated in a written power-of-attorney to legally act for another person is typically called an agent. The individual granting the power is known as the principal. This legal arrangement allows the agent to make decisions on behalf of the principal, such as in the case of a health care proxy, where the agent is authorized to make medical decisions if the principal is unable to do so themselves. It is important to note that an executor is related to the administration of a deceased person's estate, whereas a delegate usually refers to a representative who is authorized to vote or act on behalf of others.