Sir William Orpen, November 27, 1878–September 29, 1931, was an Irish painter born in Stillorgan, County Dublin. He studied at the Dublin Metropolitan School of Art and at the Slade School of Fine Art in London, where his teachers included Henry Tonks, Philip Wilson Steer, and Frederick Brown.

Orpen worked between Dublin and London, taught at the Dublin Metropolitan School of Art, and became a prominent portrait painter. He was also an official war artist on the Western Front during the First World War; major collections of his work include the Imperial War Museums, Tate, the National Gallery of Ireland, and the Metropolitan Museum of Art.

After the war, Orpen continued to paint portraits in London and Paris and became a Royal Academician. He was appointed KBE in 1918. He died in London and was buried in Putney Vale Cemetery.