Wilhelm Külz was a German liberal politician of the National Liberal Party, the German Democratic Party (DDP) and later the Liberal Democratic Party of Germany (LDPD). He held public office both in the German Empire and in the Weimar Republic. In 1926, he served as interior minister of Germany in the cabinets of chancellors Hans Luther and Wilhelm Marx.

The German Democratic Party was a liberal political party in the Weimar Republic, considered centrist or centre-left. Along with the right-liberal German People's Party, it represented political liberalism in Germany between 1918 and 1933. It was formed in 1918 from the Progressive People's Party and the liberal wing of the National Liberal Party, both of which had been active in the German Empire.