Duke of Finland (; ) was an occasional medieval title granted as a tertiogeniture to the relatives of the King of Sweden between the 13th and 16th centuries. It included a duchy along with feudal customs, and often represented a veritably independent principality. Grand Duke of Finland was a nominal royal title used by Swedish monarchs from the 1580s until 1720, which was revived again briefly from 1802 to 1805 (then as Grand Prince of Finland) and was also used by Russia's monarchs until 1917.
History of actual duchy
Bishop-Duke Kol
In the late 15th century, historian Ericus Olai claimed that Bishop Kol of Linköping (died about 1196) had been the Duke of Finland (Dux Finlandiae). In the late 12th century in Sweden, the Latin title "dux" was still used in the meaning of jarl and came to mean duke only a hundred years later (see Swedish duchies). Ericus Olai's claim is not supported by other sources. However, some historians date the small Stenberga Castle in Masku to the late 12th century, when the Novgorodian wars reached Finland and may have resulted in a temporary Swedish military presence in the area.
Noteworthy is also that the Bishop of Linköping had some sort of connection to eastern activities during the 13th century. The Pope used him in 1229 to assist the Bishop of Finland in organizing the diocese, and the first known Duke of Finland, Benedict, soon after his nomination was also elected Bishop of Linköping. The Bishop of Linköping had also accompanied the Swedish ledung on their unsuccessful Estonian expedition.
Bishop-Duke Benedict Birgerson
Benedict (1254–1291), an eccleasiastic, the youngest brother of king Valdemar I of Sweden was granted the Duchy of Finland about 1284 by a subsequent brother on the throne, King Magnus III. Benedict's appointment ended a 35-year-long period of episcopal rule in Finland, effective since the Second Swedish Crusade around 1249.
Benedict's local reign did not last long. The Duke, a consecrated priest and the Chancellor of the Realm, was elected Bishop of Linköping in 1286. As far as is known, he bore revenues from Finland until his death but did not attempt any independent rule there. He was the first known holder of the appanage of Finland.
Duke Valdemar
The youngest son of the late King Magnus III of Sweden (1240–90), Valdemar (1280s-1318), was given his late uncle Benedict's Duchy of Finland at the coronation of his eldest brother King Birger of Sweden in 1302. Valdemar's elder brother Duke Eric in the 1310s was establishing a truly independent principality in Western Sweden, Duke Valdemar being his ally. There is no evidence that Duke Valdemar succeeded in having as independent a position as Eric, but it is obvious that Valdemar used his ducal revenues to assist Eric's campaign against the King and kept his Finnish appanage and administration under Eric instead of the King.
In 1315, in alliance with Eric, Valdemar gained Turku castle and Häme Castle together with their provinces, that is most of Finland, as well as Stockholm Castle, most of Uppland and Borgholm with Öland, as the result of their revolt against the King. On December 10, 1317 he was imprisoned by King Birger in Nyköping together with Eric. Sometime in 1318, Dukes Valdemar and Eric died while incarcerated.
With his second wife Ingeborg of Norway, Duke Valdemar had a son, born in 1316, who is assumed to have died as a child.
Duke Benedict Algotson
Lord Benedict Algotsson (1330–60), accused for political reasons by Saint Bridget of being a homosexual lover of King Magnus IV of Sweden (nephew of Duke Valdemar above), had already in 1353 been recognized as Duke of Halland, originally a Danish principality, and in 1353 or 1354 also was given the Duchy of Finland.
The Duke apparently never seriously attempted to establish himself as ruler of Finland, being satisfied to bear revenues from the duchy. He had his seat in Southern Sweden, where he also acted as Viceroy of Scania.
The Duke became the victim of certain nobility's opposition to King Magnus, was exiled in 1357, and killed without an heir in 1360. In 1357, his holdings, including Finland, had been given (without the title) to King Eric, then co-ruler with Magnus. Eric did not need the ducal title, and it was then vacant almost 200 years.