Which document or legal instrument can designate who will execute an individual’s estate upon their death?

A will is a legal instrument that outlines how an individual's assets and estate should be distributed upon their death and designates an executor responsible for carrying out those wishes. The executor manages the probate process, ensuring that debts are settled, beneficiaries receive their inheritance, and any other directives specified in the will are followed.

The other options serve different purposes. A power of attorney is used to designate someone to make decisions on behalf of an individual while they are still alive, particularly in financial or medical matters, but it becomes void upon death. A deed typically pertains to the transfer of property ownership and does not address the management of an estate after someone's death. A trust, while it can manage and distribute assets upon someone's passing, involves a different legal structure and is not the primary document used for appointing an executor like a will does. Therefore, the will is the correct answer as it specifically provides the authority needed to appoint an executor for the estate.