Klopfer was an attorney and early member of the NSDAP (Nazis) with the honorary SS rank of Oberfuhrer (Brig. General). He represented Martin Bormann at the Wannsee Conference on January 20, 1942, in which the details of the 'Final Solution' against the European Jews were formalized.
After the war, he was charged with war crimes but released for lack of evidence. He became a tax advisor. He was the last surviving attendee of the Wannsee Conference, passing away in 1987.