Joachim Wolff lived in the hotel in which Bernice Summerfield worked on Guernsey in 1941. He was the head of the Prisoner of War camp and tortured Benny. He thought that Benny was mad because she told him that she came from the future as he believed that Germany was destined to win the war. He attempted to issue an ultimatum to the British Government to surrender to German authority or the Reich's new weapon would destroy the country, but he was badly beaten by Roz, who literally poked out one eye.
After the stealth plane was destroyed by Chris, the Doctor spoke with Wolff in prison, and although the exact nature of the conversation was unclear, Wolff was later found dead in a manner that suggested suicide. (AUDIO: Just War)