Wilhelm Richard Wagner (22 May 1813  – 13 February 1883) was a German composer, conductor, theatre director and essayist, primarily known for his operas (or "music dramas", as they were later called). Unlike most other opera composers, Wagner wrote both the music and libretto for every one of his works.

Wagner's compositions, particularly those of his later period, are notable for contrapuntal texture, rich chromaticism, harmonies and orchestration, and elaborate use of leitmotifs: musical themes associated with particular characters, locales or plot elements. Wagner pioneered advances in musical language, such as extreme chromaticism and quickly shifting tonal centres, which greatly influenced the development of European classical music.

He transformed musical thought through his idea of Gesamtkunstwerk ("total artwork"), the synthesis of all the poetic, visual, musical and dramatic arts, epitomized by his monumental four-opera cycle Der Ring des Nibelungen (1876). To try to stage these works as he imagined them, Wagner built his own opera house, the Bayreuth Festspielhaus.

Wagner drew largely from Northern European mythology and legend, notably Icelandic sources such as the Poetic Edda, the Volsunga Saga and the German Nibelungenlied. Through his operas and theoretical essays, Wagner exerted a strong influence on the opera world of the later nineteenth century. He was an advocate of what he called "music drama", in which all musical poetic and dramatic elements were to be fused together. Unlike other opera composers, who generally left the task of writing the libretto (the text and lyrics) to others, Wagner wrote his own libretti, which he referred to as "poems".

Further, Wagner developed a compositional style in which the orchestra's role is equal to that of the singers. The orchestra's dramatic role, in the later operas, includes the use of leitmotifs, musical themes that can be interpreted as announcing specific characters, locales, and plot elements; their complex interweaving and evolution illuminates the progression of the drama.

Wagner's later musical style, with its unprecedented exploration of emotional expression, introduced new ideas in harmony and melodic process and operatic structure. Notably from Tristan und Isolde onwards, he explored the limits of the traditional tonal system that gave keys and chords their identity, pointing the way to atonality in the 20th century. Some music historians date the beginning of modern classical music to the first notes of Tristan, the so-called Tristan chord.^[8]