Karl Harald Wiik (1883-1946) was a Swedish-speaking Finnish Social Democratic (SDP) leader.
Elected to parliament numerous times between 1911 and the time of his death and Secretary of the SDP for more than a decade, Wiik is remembered as one of six radical SDP members of parliament expelled from the SDP in the aftermath of the Winter War with the Soviet Union.
Imprisoned during the years of World War II, Wiik was released in 1944, becoming a leader of the Finnish People's Democratic League (SKDL), a left wing political organization dominated by the newly legalized Communist Party of Finland (SKP).