The agent acting under a power of attorney is known as:

The individual designated to act on behalf of another under a power of attorney is referred to as an "Attorney in Fact." This term specifically describes a person authorized to act on another's behalf in legal or financial matters, as dictated by the power of attorney document. The power of attorney grants the Attorney in Fact the ability to make decisions and execute documents for the principal, who is the person granting the authority.

It is essential to note that the Authority granted can be broad or limited, depending on the terms set forth in the power of attorney. This role emphasizes the fiduciary relationship, where the Attorney in Fact must act in the best interests of the principal and adhere to the terms specified within the power of attorney.

While similar terms like "Agent in Fact" might be used informally, "Attorney in Fact" is the correct terminology used in legal contexts to ensure clarity regarding the powers being exercised on behalf of another person. Other options might refer to legal professionals or roles but do not specifically encapsulate the function outlined in the question.