The presented biographical sketch has been devoted to Kazimierz Zakrzewski, who is little known nowadays. Born in 1900 in Cracow, K. Zakrzewski was growing up in an intellectual environment since his childhood, his father was a physics teacher, his mother a writer, and his uncle Stanislaw was an outstanding historian. Brought up at home that cherished patriotic traditions and where involvement in social matters was seen as an indication of a civic attitude, Kazimierz was trying to accomplish his scientific ambition and remain faithful to the values he had been raised to believe in throughout all his adult life. After graduating from university and completing a grant in France, young K. Zakrzewski started to work as a scientist at Jan Kazimierz University in Lvov. He achieved a status of a leading Polish specialist on Byzantium's history very quickly. In 1935 he held a post of head of the Chair of Byzantium Studies, the first one in the II Republic of Poland, which was then established at the Warsaw University. Apart from scientific activity, K. Zakrzewski was also vigorously engaged in social and political activity. Not being involved as much in the current political activity, he continued to enjoy undisputable respect as a theoretician of syndicalism. During the World War II K. Zakrzewski, in accordance with his life credo, organized underground structures of syndicalism movement at the same time taking up a job in 'Biuro Informacji i Propagandy Komendy Glównej Zwiazku Walki Zbrojnej' (Bureau of Information and Propaganda of the Headquarters of Union of Armed Struggle). Arrested by Gestapo at the beginning of 1941, he was executed by firing squad in Palmiry only two months later.