Louis-Joseph Diémer, circa 1860s, by Étienne Carjat.
Louis Joseph Diémer (14 February 1843 – 21 December 1919) was a French pianist and composer. He was the founder of the Société des Instruments Anciens in the 1890s, and also gave recitals on the harpsichord. His output as a composer was extensive, including a piano concerto and a quantity of salon pieces.