Final answer:
A health care proxy is the person legally designated to make health care decisions for a patient who is unable to do so, often appointed through a living will.
Step-by-step explanation:
The person who is legally designated to make health care decisions for a patient when they are unable to do so is known as a health care proxy. This individual is appointed through a legal document, ensuring that the patient's medical decisions are in trusted hands according to their wishes, especially if they are unable to communicate. A health care proxy is an important aspect of a living will, which may detail specific interventions a person wants or does not want, such as a Do Not Resuscitate (DNR) order. The choice of a health care proxy is guided by the principle of autonomy, which honors a patient's right to self-determination in healthcare decisions.