Jacob Zeilin was the United States Marine Corps' first non-brevet flag officer. He served as the seventh commandant of the United States Marine Corps, from 1864 to 1876.

The commandant of the Marine Corps (CMC) is normally the highest-ranking officer in the United States Marine Corps. It is a four-star general position and a member of the Joint Chiefs of Staff. The CMC reports directly to the secretary of the Navy and is responsible for ensuring the organization, policy, plans, and programs for the Marine Corps as well as advising the president, the secretary of defense, the National Security Council, the Homeland Security Council, and the secretary of the Navy on matters involving the Marine Corps. Under the authority of the secretary of the Navy, the CMC designates Marine personnel and resources to the commanders of unified combatant commands. The commandant performs all other functions prescribed in Section 8043 in Title 10 of the United States Code or delegates those duties and responsibilities to other officers in his administration in his name. As with the other joint chiefs, the commandant is an administrative position and has no operational command authority over United States Marine Corps forces.