The German Democratic Party, or Deutsche Demokratische Partei (DDP), was founded by leaders of the former Progressive People's Party (Fortschrittliche Volkspartei) and the left wing of the National Liberal Party (Nationalliberale Partei) in the early days of the Weimar Republic. Their leaders included Walther Rathenau, Eugen Schiffer, Otto Preuss, Otto Gessler, Max Weber and Erich Koch-Weser.
The Democrats were a left-wing liberal party, whereas the German People's Party was right-wing liberal. Along with the Social Democrats and the Centre Party, the Democratic party was most committed to maintaining a democratic, republican form of government. The party was attacked by some for being a party of Jews and professors (and, indeed, Jews formed one of its most loyal constituencies).
Dr. Hjalmar Schacht, once a great supporter of this party, defected to the Nazi party in 1933, believing that Hitler was a politician who, unlike those of the DDP, might save Germany by supporting a strong economy in a sound state.
The Democrats did well in the first Reichstag election, and joined the first government of the Weimar Republic as part of the Weimar Coalition of Philipp Scheidemann. They resigned from the government to protest the Treaty of Versailles later that year, but soon returned. In later elections, their showing consistently worsened. An attempted merger with the Young German Order to form the German State Party in 1930 failed miserably, and the party's Reichstag delegation became practically insignificant. The party was banned by the Nazis in 1933.