Georg Joseph Vogler was a minor composer, but a major figure in music theory in the eighteenth century. His father was the violinist and instrument maker of the Prince-Bishop of Würzburg. He is presumably not related to the composer Georg Vogler (1585 -- 1635), also of Würzburg, since that Georg Vogler was, like the subject of this article, a priest. Our subject received his education from city elementary schools, the Jesuit gymnasium, and the University in Würzburg, studied law, and had three years of theology in Bamberg. In 1771 Vogler became almoner at the Mannheim court of Elector Carl Theodor, who provided the means for him to study in Italy after Vogler wrote a successful opera called The Merchant of Smyrna. While in Rome, Vogler was ordained. When he returned, he was appointed both vice-Kapellmeister and spiritual counselor to Carl Theodor. The Elector had already made Mannheim a center for orchestral music in Germany. Now Vogler established the Mannheim Tonschule, which he intended as the first systematic institute for music. His career as a musician took him to posts in the Royal services of Munich and Sweden, and he toured extensively, even to such unlikely corners of Europe as Gibraltar and Greece (then still under Ottoman rule), and into North Africa for a study of the origins of Western European chant. He researched deeply into the Western musical system. He determined the mathematical relationships between notes more precisely than ever with his Octochord, an eight-stringed device with movable bridges. He determined several principles that are at the root of current music theory, including the idea that any complex chord can be reduced to a root, third, and fifth (in other words, a common triad). He also outlined a way that from any tone there are forty-four possible modulations. This theory of progressive modulations lay at the root of the Romantic Era's new ideas about tonality.