The Bishop of Turku (episcopus Aboensis) was the medieval Christian religious leader of Finland.
Influenced by papal bulls Swedish magnates in the 12th century set up crusade expeditions to convert the heathens in the eastern Baltic. This resulted in the establishment of the Catholic Church, the Christian religion and the Swedish conquest of Finland. Turku, or Aboa, Åbo, became the principal city in Finland and site of a bishopric.
The Protestant Reformation in the 16th century made the Catholic Church give way to the Lutheran state church established by King Gustav I of Sweden, whose principal reformer in Finland was Mikael Agricola and from 1554 also the bishop. See Lutheran Diocese of Turku.
With the creation of the Finnish state at the Diet of Porvoo in 1809, the Bishop of Turku was elevated to the position of the archbishop of the Evangelical Lutheran Church of Finland, as the Archbishop of Turku.