Sir Arthur Seymour Sullivan MVO (13 May 1842 – 22 November 1900) was an English composer, of Irish and Italian descent, best known for his operatic collaborations with librettist W. S. Gilbert, including such continually-popular works as H.M.S. Pinafore, The Pirates of Penzance, and The Mikado. Sullivan's artistic output included 23 operas, 13 major orchestral works, eight choral works and oratorios, two ballets, incidental music to several plays, and numerous hymns and other church pieces, songs, parlour ballads, part songs, carols, and piano and chamber pieces.

Apart from his comic operas with Gilbert, Sullivan is best known for some of his hymns and parlour songs, including "Onward Christian Soldiers", "The Absent-Minded Beggar", and "The Lost Chord". His most critically-praised pieces include his Irish Symphony, his Overture di Ballo, The Martyr of Antioch, The Golden Legend, and, of the Savoy Operas, The Yeomen of the Guard. Sullivan's only grand opera, Ivanhoe, was initially highly successful, but it has been little heard since his death.

Sullivan was born in Lambeth, London. His father, Thomas Sullivan (1805–1866), was a military bandmaster and music teacher born in Ireland, who was educated in Chelsea, London and was based for some years at the Royal Military Academy Sandhurst. Here Arthur became proficient with all the instruments in the band by the age of eight. His mother Mary Clementina (née Coghlan, 1811–1882) was English, of Irish and Italian descent. While studying at a private school in Bayswater, Sullivan convinced his parents and the headmaster, William Gordon Plees, to allow him to try out for the choir of the Chapel Royal. Despite concerns about Sullivan's age, which would limit how long he could serve before his voice began to change, he was accepted and soon became a soloist. Sullivan flourished under the training of Reverend Thomas Helmore, the master of the choristers, and began to compose anthems and songs. Helmore arranged for one of these, "O Israel", to be published by Novello in 1855 – Sullivan's first published work. Helmore also enlisted Sullivan's assistance in creating harmonisations for a volume of The Hymnal Noted.