Short answers, pulled from the story.
Führer means "leader" or "guide" in German. It remains common in German compound words such as Reiseführer (travel guide), Führerschein (driver's license), and Museumsführer (museum guide), but standing alone in a political context it carries strong negative connotations due to its association with Adolf Hitler.
Hitler received the title Führer within the Nazi Party in 1921. He resigned from the party in protest over founder Anton Drexler's plan to merge with another group, and the party's Executive Committee gave in to his demand to be made chairman with dictatorial powers as the condition for his return.
Georg Ritter von Schönerer (1842-1921), an Austrian pan-German nationalist, was the first known political figure to be addressed as the Führer by his followers. Historian Richard J. Evans credits Schönerer's Pan-German Association with likely introducing the term to the German far-right.
One day before President Paul von Hindenburg died in 1934, Hitler's cabinet issued the "Law Concerning the Head of State of the German Reich," which merged the presidency with the chancellorship upon Hindenburg's death. A referendum on the 19th of August 1934 approved the arrangement. Hitler styled himself Führer und Reichskanzler, though Reichskanzler was later dropped from everyday usage.
On the 23rd of June 1941, Hitler declared himself the Germanischer Führer, or Germanic Führer, asserting leadership over all peoples the Nazis classified as the Nordic-Germanic master race, including Norwegians, Danes, Swedes, and Dutch. Dutch fascist Anton Mussert formally addressed Hitler by this title during a visit to the Reich Chancellery in Berlin on the 12th of December 1941.
Ein Volk, ein Reich, ein Führer means "One People, One Empire, One Leader" and was one of the most repeated Nazi political slogans. A historian describes it as leaving "an indelible mark on the minds of most Germans who lived through the Nazi years," appearing on posters, in publications, and in constant radio broadcasts. It expressed the Führerprinzip's claim of absolute authority over every sector of German society.