Info below includes definition of Representative Payee, how to request one from the Social Security Administration, and how to designate one in advance of possibly needing one.

Representative Payee
https://www.ssa.gov/payee/?tl=4
Social Security's Representative Payment Program provides benefit payment management for our beneficiaries who are incapable of managing their Social Security or Supplemental Security Income (SSI) payments. We appoint a suitable representative payee (payee) who manages the payments on behalf of the beneficiaries. Generally, we look for family or friends to serve as payees. When friends or family members are not able to serve as payees, we look for qualified organizations. We also offer the option to advance designate up to three individuals who could serve as payee for you if the need arises. If you are concerned that someone you know becomes incapable of managing or directing the management of his or her benefits, please call us at 1-800-772-1213 (TTY 1-800-325-0778) to request an appointment to discuss your concerns.

Frequently Asked Questions (FAQs) for Representative Payees
https://www.ssa.gov/payee/faqrep.htm?tl=5
What is a Representative Payee?
A representative payee is a person or an organization. The Social Security Administration appoints a payee to receive the Social Security or SSI benefits for anyone who can’t manage or direct the management of his or her benefits. A payee’s main duties are to use the benefits to pay for the current and future needs of the beneficiary, and properly save any benefits not needed to meet current needs. A payee must also keep records of expenses. When we request a report, a payee must provide an accounting to us of how he or she used or saved the benefits.
 
NOTE
Being an authorized representative, having power of attorney, or a joint bank account with the beneficiary is not the same as being a payee. These arrangements do not give legal authority to negotiate and manage a beneficiary's Social Security and/or SSI benefits. In order to be a payee, you must apply for and be appointed by Social Security.
 
What About "Power of Attorney"?
Power of attorney is a legal process where one individual grants a third party the authority to transact certain business for that individual. It does not lessen the rights of the individual and does not usually grant the third party the right to manage the individual's assets. It typically makes no finding about the individual’s capability or competence. The Treasury Department does not recognize power of attorney for negotiating federal payments, including Social Security or SSI checks.
 
This means, if you have power of attorney for someone who is incapable of managing his or her own benefits, you must still apply to serve as his or her payee.

Advance Designation of Representative Payee
https://www.ssa.gov/payee/advance_designation.htm
To help protect what is important to you, we offer the option to advance designate a representative payee. Advance designation allows you to designate up to three individuals who could serve as a representative payee for you if the need ever arises.
We offer advance designation to capable adults and emancipated minors who are applying for or receiving Social Security benefits, Supplemental Security Income, or Special Veterans Benefits. If you become unable to manage, or direct others to manage your benefits in the future, you will have peace of mind knowing that someone you trust may be appointed to manage your benefits for you.