This is an extended study of the historical significance, life, and music of Nikolai Kapustin, Russian composer and pianist. Kapustin's music creatively fuses the virtuosity and structure of traditional classical music with the musical language of jazz. Having composed over 147 works, including twenty piano sonatas, twenty-four preludes and fugues, and six piano concerti, he is arguably one of the most prolific composers of the twentieth and twenty-first centuries. The study consists of three parts. The first part is an overview of the history of classical-jazz fusion and illustrates how Kapustin stands apart from composers whose music is typically categorized as "crossover" or "third stream." The second part documents Kapustin's biography and musical development throughout the various stages of his life and is the most thorough account of Kapustin's career to date. The third part presents an analysis of the combination of jazz and classical styles in two contrasting pieces: Kapustin's Sonata No. 2, Op. 54, and his Prelude and Fugue Op. 82, No. 10. As a preface, this part will also include an overview of some basic jazz compositional techniques that will help the reader understand the analyses.