William Sommer was an American Modernist painter.

William Sommer was born in Detroit, Michigan in 1867. He was largely self-taught, but received instruction early on from artist and commercial lithographer Julius Melchers. He apprenticed with the Detroit Calvert Lithograph Company for seven years but in 1890 he traveled to Europe where he trained with Professors Johann Herterich, Ludwig Schmid, and Adolph Menzel. In 1907 he accepted a position with the Otis Lithograph Company of Cleveland, Ohio and in 1911 he co-founded the Kokoon Arts Club to promote modern art in Cleveland. In 1914 he relocated to Brandywine, Ohio. He worked on several large-scale murals for the Federal Art Project, including Rural Homestead in the Geneva, Ohio post office.