German-born American conductor who was largely responsible for the role of symphony orchestras in many American cities.

A violin prodigy, Thomas moved with his family to New York City, where he was to become a shaping force in practically every aspect of the city's musical life. While in his 20s, he instituted a chamber-concert series that drew praise from both sides of the Atlantic, and he also conducted for the Brooklyn Philharmonic. In 1862 he initiated the Irving Hall Symphonic Soirées and a year later began an outdoor summer series. The Theodore Thomas Orchestra set out in 1869 on the first of its North American tours.

Thomas was appointed conductor of the New York Philharmonic in 1877, leaving for a short period to found the Cincinnati College of Music (1878–80). In 1891 the enticement of forming a full-time resident orchestra took him to Chicago, and he led the Chicago Symphony Orchestra until his death. His interpretations of the standard repertoire were highly respected, and he premiered works of many contemporaries, including Pyotr Ilyich Tchaikovsky, Johannes Brahms, and Richard Strauss.