Karel Jaroslav Obrátil, often referred to as K. J. Obrátil, was a Czech cultural worker, journalist, writer, poet, translator, and publisher. He also wrote under the pseudonyms ABC, Alfa, Karel Jaroš, and Jaroslav Olšanský.

He is sometimes mistakenly confused with the collector and editor of Bezruč's works, Jaromír Obrátil (who published, among other works, Pseudobezruč, 1935, and Bezručův národní zpěvníček, 1940). The similarity of his first names to those of Erben leads to him being mistakenly listed as Karel Jaromír in various dictionaries and databases.

He worked as a school director in Uherské Hradiště. According to the author of the afterword to Velký slovník sprostých slov (The Great Dictionary of Dirty Words), Jan Hýsek, he was subject to disciplinary proceedings for over four years due to his involvement with pornography, after which he was finally fully rehabilitated, but continued to be socially ostracized, which is why he moved permanently to Prague in 1926.

He made no secret of his anti-fascist views, which went unpunished for a long time, but he was eventually arrested by the Gestapo on March 6, 1945, and taken to their Prague headquarters in Pečkárna. A month later, on April 5, 1945, he died as a result of torture in the prison hospital in Pankrác. His most important work is the three-volume Kryptadia, originally published as a pamphlet, reissued by Paseka in 1999-2000, and under more reader-friendly titles Velký slovník sprostých slov (Great Dictionary of Dirty Words, vol. 3) and První a Druhá Kytice národních prasáren (First and Second Bouquet of National Filth, vols. 1+2) by Lege artis (1999-2017). A selection from Kryptadia was also published by Ivan Wernisch under the title Kdo to čte, je prase (Whoever reads this is a pig, 2008).