Also featuring Emily Blunt (Katherine "Kat" Oppenheimer), Casey Affleck (Boris Pash) and Florence Pugh (Jean Tatlock), was shot on large format film stock, specifically made to fit IMAX screens.

Source: https://www.cbr.com/oppenheimer-first-look-footage-cillian-murphy/

Colonel Boris Pash played a role in investigating Oppenheimer for potential espionage and communist ties, leading to Oppenheimer's disgrace in the public eye.

Source: https://screenrant.com/oppenheimer-boris-pash-what-happened-after/