Karl Yulievich Davydov (15 March [O.S. 3 March] 1838 – 26 February [O.S. 14 February] 1889) was a Russian cellist of great renown during his time, and described by Pyotr Ilyich Tchaikovsky as the "tsar of cellists". Arensky dedicated his first piano trio to Davydov's memory. He was also a composer, mainly for the cello. 

In his youth he studied mathematics at St. Petersburg University, and then pursued a career as a composer, studying with Moritz Hauptmann at the Leipzig Conservatory. He became a full-time cellist in 1850 while continuing to compose in his spare time. He later became head of the St Petersburg Conservatory. He had many students, including Aleksandr Verzhbilovich.

In 1870 Count Wilhorsky, a patron of the arts, presented Davydov with a Stradivarius cello constructed in 1712. This cello, now known as the Davidov Stradivarius, was owned by Jacqueline du Pré until her death and is currently on loan to cellist Yo-Yo Ma.

He intended to write an opera on the subject of Mazeppa. Viktor Burenin wrote a libretto for this purpose in 1880, but when Davydov proved unable to find the time to compose, Burenin offered the libretto to Tchaikovsky.

Although closely associated with Tchaikovsky, Karl Davydov was not related to the Davydov clan into which Tchaikovsky's sister Alexandra married. Davydov died in Moscow on February 26, 1889.

Davydov (also appeared in different spellings: Davidoff / Davidov) transcribed and arranged Chopin's solo piano works for violoncello and piano accompaniment. Transcription albums of Walzer and Mazurkas published by Breitkopf & Härtel. Another transcription album is a selection of Nocturnes and others solo piano works published by Edition Peters.