Karel Hašler (31 October 1879 in Prague – 22 December 1941 in Mauthausen) was a Czech songwriter, actor, lyricist, film and theatre director, composer, writer, dramatist, screenwriter and cabaretier.

[6] In 1942, in his last film role, he played himself in Za tichých nocí (In the Quiet Nights), made by his son Gina Hašler.

In September 1941, during production of the film Městečko na dlani, based on the script by Jan Drda, he was arrested by the Gestapo and sent to the Mauthausen concentration camp.

[9][6][10] In the post-war Communist Czechoslovakia he was officially ignored for political reasons, because many of his songs hailed Tomáš Masaryk and Czechoslovak Legionnaires and mocked interbellum communists, and also because he was an admirer of the founder of the National Fascist Community Radola Gajda, and ideologically was close to the interbellum Czech fascists.

[17] In 2008, Czech directors Marek Jícha and Josef Lustig made a documentary Písničkář, který nezemřel (The Immortal Balladeer of Prague) describing the fate of Hašler's illegitimate son Thomas Hasler.

[18] On the occasion of Hašler's 130th anniversary (2009) a monument by sculptor Stanislav Hanzík was unveiled at the Old Castle Steps [cs].

With his engaged patriotic approach he helped to strengthen the national consciousness of Czech people during times of danger and oppression.