Prince Frederick of Hesse (May 1, 1868 - May 28, 1940), Friedrich Karl Ludwig Konstantin, Prinz und Landgraf von Hessen, brother-in-law to Emperor Wilhelm II of Germany and elected king of Finland (October 9, 1918).

In the Finnish election document the prince is called Fredrik Kaarle, but according to conventional wisdom his name as king would have been Väinö I of Finland. Although the correctness of this name is not quite undisputed, it is manywhere repeated, for instance at Finland's parliament's official web-site[1].

On November 11, 1918, the armistice between the warring fractions of World War I was signed, and two days earlier Kaiser Wilhelm had abdicated and Germany was declared a Republic. Germany's defeat in the war, and the stated fact that none of the allies would ever accept a German-born prince as the king of Finland, led Frederick to finally renounce the throne on December 14, 1918, and subsequently for Finland to also adopt a republican constitution.