Background
Kossak was born in Drohobych in Galicia (then of the Austro-Hungarian Empire, now in Ukraine).
Kossak was born in Drohobych in Galicia (then of the Austro-Hungarian Empire, now in Ukraine).
He studied law at Lviv University and was one of the organizers of the nationalist movement in Galicia.
He became deputy commander of the Carpathian Sich National Defense Organization in Carpatho-Ukraine. He was killed in action by Hungarian troops in Solotvyna, near Bukshtyn, in Transcarpathia.
He was a member of the Ukrainian Military Organization in the late 1920s where he directed the "combat", then the organizational, activities of the Organization of Ukrainian Nationalists in 1939 as a member of its Home Executive.