The name that you need to put in this blank is Adolph Hitler. Hitler was, of course, the dictator of Germany during the time that the Nazi Party ruled that country.
Hitler had served as a soldier in WWI. After the end of that war, he was pretty unhappy with the way Germany was going so he joined the Nazi Party and soon rose to a position of power in that party. At that time, it was a very small party.
The party tried to overthrow the Germany government in 1923. For that, Hitler was imprisoned. While in prison, he started to compose Mein Kampf.