James Hamilton Siree Clarke (25 January 1840 – 9 July 1912), better known as Hamilton Clarke, was an English conductor, composer and organist. Although Clarke was a prolific composer, he is best remembered as an associate of Arthur Sullivan, for whom he arranged music and compiled overtures for some of the Savoy Operas, including Gilbert and Sullivan's The Mikado.
Clarke began as an organist, pianist and theatre conductor, becoming a musical director for Gilbert and Sullivan, among others. While conducting at London theatres, he also composed a tremendous volume of church music, organ solos, songs, operettas and orchestral works. Beginning in the late 1870s, he composed incidental music as musical director for many of Henry Irving's spectacular productions at the Lyceum Theatre. He also composed music for many of the German Reed Entertainments and conducted at many other London theatres in the 1870s and 1880s. Clark published a Manual of Orchestration and music criticism, as well as some fiction. In 1889, he took charge of the Victorian National Orchestra in Australia, returning to England in 1892 and soon becoming conductor of the Carl Rosa Opera Company for several years.