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.
Karl Muck was born in Darmstadt, Germany. Muck's father, a senior court official and amateur musician, moved the family to Switzerland in 1867 and acquired Swiss citizenship. Karl Muck acquired Swiss citizenship when he was 21. Muck studied piano as a child and made his first public appearance at the age of 11 when he gave a piano solo at a chamber music recital. He also played the violin in a local symphony orchestra as a boy. He graduated from the gymnasium at Würzburg and entered the University of Heidelberg at 16. In May 1878 he entered the University of Leipzig, where he took his degree as Doctor of Philosophy in 1880. While there studied music at Leipzig Conservatory. He made his formal debut as a concert pianist on February 19, 1880 at the Leipzig Gewandhaus in Xaver Scharwenka's Piano Concerto No. 1 in B-flat minor with Arthur Nikisch conducting.
He began his conducting career in comparatively minor provincial cities, starting in 1880 as Second Conductor (Zweiter Kapellmeister) in Zurich (Aktientheater), moving to Salzburg (k.k. Theater) in October 1881 as Principal Conductor (Erster Kapellmeister), where he served until April 1882. He then held appointments in Brünn (Stadttheater: October 1882 to June 1883) and Graz (1884–1886), where he married 21-year-old Anita Portugall on February 3, 1887. His first position in a major musical center came in Prague as Principal Conductor at Angelo Neumann's Deutsches Landestheater, starting with a performance of Die Meistersinger on August 15, 1886, and ending in June 1892. He also conducted Neumann's traveling opera company, appearing at Berlin and in 1888–1889 conducting Wagner's Ring cycle in Moscow and St. Petersburg. He left Prague to become principal conductor in October 1892 of the Berlin Court Opera (Kgl. Oper — today the Berlin State Opera, where he was appointed Chief Musical Director (Kgl. preussischer Generalmusikdirector) on August 26, 1908. He remained in Berlin until 1912, conducting 1,071 performances of 103 operas. He also conducted the Royal Orchestra in concerts there.