John Casimir (October 16, 1898 – January 3, 1963) was an American jazz clarinetist and bandleader, best remembered as the leader of The Young Tuxedo Brass Band for some 20 years up to his death. Casimir started playing professionally with the Young Eagles Band with Lee Collins in 1919. He was also a member of the Original Tuxedo Brass Band, often following the lead of Louis Armstrong. The Young Tuxedo Brass Band's 1958 album was released under the title Jazz Begins by Atlantic Records. It was the only recording the band released under Casimir's leadership. He also led a dance band using some of the same musicians under the name the Young Tuxedo Jazz Band, which also recorded. He played Bb clarinet with the jazz band and the distinctive higher Eb clarinet with brass bands.

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