In the more than 70 years since Hitler's death, countless books and TV documentaries have tried to approach the life of the man from Braunau in Upper Austria and explain the "phenomenon" of Adolf Hitler. But his biography has never been told in this way before: In "Who was Hitler" only contemporaries and Hitler himself have their say. Their statements from diaries, letters, speeches and autobiographies are assembled with new, largely unpublished archive material. Only original films are used - mainly amateur footage and often in colour - and some photographs, no interviews, no re-enacted scenes, no explanatory graphics, no technical gimmicks and no omniscient experts. Hitler's life and work is thus reflected in a unique way in the social picture of the years 1889 to 1945 - a cinematic documentary film that shows new ways of conveying contemporary history through film. The film was based on one of the most extensive archive researches ever conducted for a TV or cinema documentary. More than 120 archives in 14 countries were evaluated, 850 hours of film were viewed, over 100 hours of 8mm, 9.5mm Pathé, 16mm or 35mm films were rescanned in HD, 2k and 2.3k, restored and technically processed. The mostly soundless film sources were dubbed true to the original to ensure a historically appropriate atmosphere. The testimonies are spoken by 125 speakers.