Karl August Fritz Schiller (24 April 1911 – 26 December 1994) was a German economist and politician of the Social Democratic Party (SPD).

He was the inventor of the magic square, depicting Economic equilibrium, and of the Concerted activity (Konzertierte Aktion) to reflate the German market.

After taking part in World War II as a soldier from 1941 to 1945, he became professor at the University of Hamburg, where he became principal from 1956 to 1958.

In the first cabinet of Willy Brandt, Schiller continued to serve in the previous position, and was also Federal Minister of Finance from 1971 to 1972 after the resignation of Alex Möller.

In 1972, he participated together with Ludwig Erhard in a CDU campaign, whereby both acted as defenders of market economy.