From Halopedia, the Halo wiki
The Commander-in-Chief of the Spartans (CINCSPAR) is an office held by the director of Spartan Operations, a service branch of the UNSC Armed Forces. In this capacity, the CINCSPAR holds the authority of a four-star general.
Rear Admiral Musa Ghanem is the current Commander-in-Chief of the Spartans. Jun-A266, the acting Chief of Staff of Spartan Operations, serves him as the branch's representative to the UNSC Security Council for routine administrative tasks.