Who is recognized as the First Marine leader?

The correct answer highlights Capt Samuel Nicholas, who is acknowledged as the first leader of the Marine Corps. He served as the first Commandant of the Marine Corps and was appointed to this position in 1775. His leadership was pivotal during the formative years of the Corps, helping to establish its traditions and combat philosophy. Nicholas's contributions laid the groundwork for the future of the Marine Corps, and his role in organizing and leading the Marines during the early conflicts solidified his historic status.

The other individuals listed, while significant within their respective contexts, either came after Nicholas or held different roles that did not establish them as the first leader of the Marine Corps. Capt Robert Mullen and Archibald Henderson were later figures in Marine history, and John P. Sousa, while well-known as a bandmaster and composer, did not have a role in military leadership.