Väinö Tanner (1881-1966), pioneer leader in Finland's Co-op Movement, became after the Civil War in Finland, in which he hadn't participated, Finland's leading Social Democratic politician, and a strong proponent of Parliamentarism. His main achievment was the party's rehabilitation after the Civil War. Väinö Tanner served as Prime Minister 1926-1927, Minister of Finance 1937-1939, Foreign Minister 1939-1940, and after the Winter War, when he according to Soviet wishes had resigned from the Foreign Ministry, as Minister of Trade 1940-1942.

To accommodate the Soviet Union, Väinö Tanner was after the Continuation War tried by a war tribunal in February 1946, and sentenced to 5½ years in prison.