Final answer:
The Social Security Administration was the New Deal agency created to aid the elderly, the disabled, and other beneficiaries, established under the Social Security Act of 1935.
Step-by-step explanation:
The New Deal agency created specifically to serve the population of the elderly, the disabled, and other beneficiaries indicated in the question is the Social Security Administration. This agency was established under the Social Security Act of 1935 as part of President Franklin D. Roosevelt's Second New Deal. Its primary purpose was to provide financial assistance and a social safety net to the most vulnerable populations, including the elderly, disabled, and unemployed, through programs such as pensions, unemployment insurance, and aid for families with dependent children. Significant expansions Medicare and Medicaid were added later under President Johnson's administration to offer health coverage to the elderly and certain disabled Americans under the age of sixty-five.