25 U.S. Code § 2 - Duties of Commissioner
The Commissioner of Indian Affairs shall, under the direction of the Secretary of the Interior, and agreeably to such regulations as the President may prescribe, have the management of all Indian affairs and of all matters arising out of Indian relations.
For transfer of functions of other officers, employees, and agencies of Department of the Interior, with certain exceptions, to Secretary of the Interior, with power to delegate, see Reorg. Plan No. 3 of 1950, §§ 1, 2, eff. May 24, 1950, 15 F.R. 3174,64 Stat. 1262, set out in the Appendix to Title 5, Government Organization and Employees.
All supervisory and appellate powers and duties in regard to Indian affairs theretofore vested in Secretary of the Treasury were thereafter to be exercised and performed by Secretary of the Interior under provisions of section 1 of act July 27, 1868, ch. 259, 15 Stat. 228.
Appointment by President of a Commissioner of Indian Affairs to act under direction of Secretary of War was provided for by section 1 of act July 9, 1832, ch. 174, 4 Stat. 564.