Wacław Kostek-Biernacki (1882–1957) was a Polish interwar politician and a popular fantasy writer (pen name Brunon Kostecki) as well as a Polish soldier of World War II, imprisoned and blacklisted in Stalinist Poland. In his youth, he was an activist in the Polish Socialist Party, and member of the secret Polish Military Organisation during World War I. Kostek-Biernacki joined the Polish Legions in World War I under Józef Piłsudski. He supported the May Coup d'État of 1926.