Karel Boleslav Jirák (Karel Bohuslav Jirák) (*January 28, 1891 in Prague, Bohemia - †January 30, 1972 in Chicago, Illinois, USA) was a Czechoslovak composer and conductor.
Jirák was born in Prague and became a pupil of Josef Bohuslav Foerster and Vítězslav Novák at the Charles University and at music academy in Prague .
From 1915 to 1918 he was the Kapellmeister at the Hamburg Opera and worked from 1918 to 1919 as a conductor at the National Theatre in Brno and Ostrava. From 1920 to 1930, he was a composition teacher at the Prague Conservatory, and principal conductor of the Czechoslovak Radio Orchestra until 1945.
In 1947, he emigrated to the USA, where from 1948 to 1967 a professor at Roosevelt University, Chicago and in 1967 a composition teacher at the Conservatory college in Chicago. He remained in this position until 1971.
Jirák's opera was Apolonius z Tyany (Apollonius of Tyana, 1912–1913), which was initially ignored by Prague's National Theatre and later accepted under the title Žena a Bůh (The woman and the god, 1936). He wrote six symphonies and several symphonic variations. In 1952 he wrote a Symphonic Scherzo for volume. He also wrote many suites and overtures, numerous pieces of chamber music, many preludes and a Suite for organ, a Requiem, choruses, and song cycles. He was a popular and renowned musical theorist.