Sergiusz Piasecki was born on April 1, 1901 (or June 1, 1899) in Lyakhavichy, then in Northwestern Krai of the Russian Empire (now Brest Province, Belarus). The latter date was presented by Piasecki on several occasions, probably because he deliberately wanted to mislead the authorities. He was an illegitimate son of a russifed Polish nobleman Michal Piasecki and a Belarusian mother Klaudia Kukalowicz, a servant working for the Piasecki family, whom Sergiusz never met. According to his own life story, he was looked after by stepmother Filomena Gruszewska, a devout Catholic, who openly disliked him. His childhood was very difficult also, because children at school mocked his Polish roots, calling him "Lach" (which, in loose translation, is the Russian equivalent of the ethnic slur Polack). Conversely, Piasecki hated the Russian school – as he later explained – and in the seventh grade, armed with a pistol attacked the Teacher. Sentenced to jail, he escaped while in prison, and thus his formal education ended.