John Philip Sousa (; November 6, 1854 – March 6, 1932) was an American composer and conductor of the late Romantic era known primarily for American military marches. He is known as "The March King" or the "American March King", to distinguish him from his British counterpart Kenneth J. Alford who is also known as "The March King". Among his best-known marches are "The Stars and Stripes Forever" (National March of the United States of America), "Semper Fidelis" (official march of the United States Marine Corps), "The Liberty Bell", "The Thunderer", and "The Washington Post".

Sousa began his career playing violin and studying music theory and composition under John Esputa and George Felix Benkert. His father enlisted him in the United States Marine Band as an apprentice in 1868. He left the band in 1875 and learned to conduct. From 1880 until his death, he focused exclusively on conducting and writing music. He eventually rejoined the Marine Band and served there for 12 years as director, after which he organized his own band. Sousa aided in the development of the sousaphone, a large brass instrument similar to the helicon and tuba.

Upon the outbreak of World War I, Sousa was awarded a wartime commission of lieutenant commander to lead the Naval Reserve Band in Illinois. He then returned to conduct the Sousa Band until his death in 1932. (In the 1920s, he was promoted to the permanent rank of lieutenant commander in the naval reserve, but he never saw active service again.)