German cellist and composer (b. 15 September 1848 in Seesen ; d. 2/14 February 1890 in Moscow), born Karl Friedrich Wilhelm Fitzenhagen; known in Russia as Vilgelm Fyodorovich Fittsengagen (Вильгельм Федорович Фитценгаген).
The son of a local music director, Fitzenhagen commenced piano lessons at the age of five, the cello at eight, and the violin at eleven; he was also proficient in several wind instruments. He studied under August Theodor Müller (1802–1875) and Friedrich Grützmacher (1832–1903), becoming a soloist at the Dresden Hofkapelle in 1868. Two years later he was invited to become cello professor at the Moscow Conservatory — a position he retained until the end of his days. Here he met Tchaikovsky, and Fitzenhagen performed many of the composer's concert pieces and chamber works. He performed at the premières of all three of Tchaikovsky's numbered string quartets (1871–1876), and of the Piano Trio, Op. 50 (1882)
Tchaikovsky's Variations on a Rococo Theme were written for Fitzenhagen in 1876, and the dedicatee took it upon himself to make drastic "'improvements" to the original score (which was not revived until the 1940s), even to the extent of excising an entire variation.
At the conservatory Fitzenhagen also taught Anatoly Brandukov, who was to become another great exponent of Tchaikovsky's cello works.
As noted above, Tchaikovsky;s Variations on a Rococo Theme for cello and orchestra, Op. 33 (1876), was dedicated to Fitzenhagen.