Together with Dominik Smole, Dane Zajc and Taras Kermauner, he was the most visible representative of the so-called Critical generation, a group of Slovenian authors and intellectuals that reflected on the paradoxes of the communist regime, and the relation between power and individual existence in general.
During World War II, Primož lived under a false identity with a temporary adoptive family, as both his father and uncles were prominent figures in the partisan resistance.
These included, among others, Taras Kermauner, Janko Kos, Dominik Smole, Dane Zajc, Veljko Rus, Jože Pučnik, Gregor Strniša, Marjan Rožanc, and others.
His best-known play is "The Affair" (Afera), set during the anti-Fascist resistance in Northern Italy, but in fact a metaphorical account of the trial against the dissident Jože Pučnik.
In the play "Dialogues" (Dialogi), set in an anonymous Eastern European country, Kozak described the paranoic atmosphere of the Stalinist show trials.