Karl Muck (October 22, 1859 – March 3, 1940) was a German-born conductor of classical music. He based his activities principally in Europe and mostly in opera. His American career comprised two stints at the Boston Symphony Orchestra. He endured a public outcry in 1917 that questioned whether his loyalties lay with Germany or the United States during World War I. Though he was a Swiss citizen, he was arrested and interned in a camp in Georgia from March 1918 until August 1919. His later career included notable engagements in Hamburg and at the Bayreuth Festival.