Patrick Sarsfield Gilmore (December 25, 1829 – September 24, 1892) was an influential Irish-born American composer, bandmaster, and soldier. Born in Ballygar, County Galway, Ireland, Gilmore immigrated to the United States in 1848, settling in Boston, Massachusetts. He quickly became a prominent figure in the American music scene, leading several bands including the Suffolk, Boston Brigade, and Salem bands. Gilmore's career was marked by his service in the Union Army during the Civil War, where he and his band enlisted and performed for the troops. He is credited with writing the lyrics to "When Johnny Comes Marching Home" under the pseudonym Louis Lambert.

Gilmore's post-war achievements included organizing monumental music festivals, such as the National Peace Jubilee in 1869 and the World's Peace Jubilee in 1872, which featured massive orchestras and renowned musicians like Johann Strauss II. These events solidified his reputation as a leading musical figure. In 1873, he moved to New York City, where he became the bandmaster of the 22nd Regiment, taking the band on successful tours of Europe.

Renowned for his showmanship and innovations in instrumentation, Gilmore played a crucial role in transitioning band music from brass-heavy compositions to those incorporating more reeds, such as clarinets. He was among the first American bandmasters to conduct arrangements of classical composers like Mozart and Liszt. Gilmore passed away in St. Louis, Missouri, in 1892, while preparing for a musical celebration of the quadricentennial of Columbus' voyage, leaving behind a legacy as a pioneer in American band music.