Kazimierz Władysław Mastalerz (20 November 1894 in Czeladź or Sosnowiec – 1 September 1939 at Krojanty) was a Polish military commander of the 18th Pomeranian Uhlan Regiment. He was the son of Jan Mastalerz (1858–1947), train driver, and née Dobke Sophia (1875–1937). He attended high school in Częstochowa. He belonged to the National Youth Organisation of Secondary Schools and the Organization of the Polish Youth "Future" (PET). In September 1912 he co-founded the scout team. At the end of 1912, as a student of class VII, he was arrested by the Russians and taken into custody in Częstochowa. After his release he moved to Warsaw, where he attended school. Fearing re-arrest, he moved to Lviv, and there continued his studies at Matura courses. In 1914, he passed the exams. During this period