Born in Warsaw on the 30th of May, 1904. In 1926, already during his studies in philosophy and history, he was formally connected with the National Democracy as a member of, among others, the All—Polish Youth and the National Union of Polish Academic Youth. He then wrote: ‘For some people, we are reactionaries, conservatives, clericalists, and fanatics; for others we are radicals, atheists, and opportunists. For us, such divisions simply do not exist. We are conservatives, true, for we believe it is necessary, and sound, to maintain and cultivate our tradition, culture, family life, and connection with our Polish past. But we are progressives, too, since we march boldly forward, rejecting, without prejudice, all that is harmful or detrimental to our nation’ (Akademik i Polityka). In 1928 Mosdorf became the head of All-Polish Youth and received his M.A. on the basis of his thesis Zygmunt Balicki’s Ethical Beliefs, and in 1934 he successfully defended his doctoral thesis on Auguste Comte’s positive philosophy which he had written under the supervision of Professor Władysław Tatarkiewicz. In the same year he also signed the Declaration of the National Radical Camp, thus becoming one of the leaders of Nationalist opposition. However, following the assassination of Minister Bronisław Pieracki, which resulted in a surge of arrests among the leaders of the National Radical Camp, Mosdorf remained at large. He left Warsaw and was hiding for more than a year. When the environment of the young nationalists was divided in the second half of the 1930’s, he managed not to get involved in those conflicts, although he kept on collaborating closely with Stanisław Piasecki, wring to his “Prosto z Mostu” weekly. In that period he also published his work Wczoraj i jutro in which he proposed his vision of a Catholic Poland. He belonged to a group of radical activists who had travelled the long road from the Nationalist fascination with paganism to full acceptation of Catholicism. In 1936, he wrote in “Prosto z Mostu”: ‘’We are fanatics; only fanatics can achieve great things. We despise the compromise: it is not only a feature of our young age, but also of the spirit of our times. Someone pursuing his own, or somebody else’s, interests, is always ready to struck a “reasonable” compromise, because his reckoning tells him that a bird in the hand is worth two in the bush. Someone championing some purely abstract theories is also likely to make concessions, if only for the sake of peace. But someone fighting for moral values is ready to destroy all the impediments in his way at any cost, irrespective of the sacrifices it takes.’ Being a radical, Mosdorf often used anti-Semitic rhetoric; however, when he got to the Auschwitz camp during the war, he did all he could to help the Jewish prisoners; at the same time, he was involved in the formation of a secret group of Nationalists in the camp. About a hundred of prisoners were engaged in its activities, including some representatives of the older generation of National Democrats, such as Roman Rybarski. Mosdorf would give secret lectures in history, keep in touch with other clandestine organizations, smuggle news into the camp, as well as various articles that were in short supply. Following a denunciation, he was moved to the notorious Barrack XI. Shortly afterwards – on the 11th of October – he was shot in a collective execution. There are many varying accounts regarding the circumstances of his death. According to one of them, Mosdorf – the Nationalist – was denounced by Józef Cyrankiewicz, the later Communist Prime Minister of Polish People’s Republic.