The Icelandic Reformation took place in the middle of the 16th century. Iceland was at this time a territory ruled by Denmark, and Lutheran religious reform was imposed on the Icelanders by King Christian III of Denmark. The Icelandic Reformation ended with the execution of Jón Arason, Catholic bishop of Hólar, and his two sons, in 1550, after which the country adopted Lutheranism.
Christian III became king of Denmark in 1535. That same year, on October 30, 1536, he formally established the Danish Lutheran Church and decreed that his Danish subjects should adopt Lutheranism. He quickly extended religious reform to the Danish-ruled territories of Norway and the Faroe Islands, but left Iceland a Catholic country for some time, making no efforts to introduce Protestant reforms in the ensuing years.
The Catholic bishops in Iceland at the time were Ögmundur Pálsson of Skálholt and Jón Arason of Hólar. They were both powerful leaders who had originally been bitter enemies, but with the approaching threat of Lutheranism, they found common cause as allies against religious reform. Denmark had been embroiled in civil war during the dissolution of the Kalmar Union, and the two Icelandic bishops had held both secular and ecclesiastical power in the country for many years.
Luther's influence had already reached Iceland before King Christian's decree. The Germans fished near Iceland's coast, and the Hanseatic League engaged in commerce with the Icelanders. These Germans raised a Lutheran church in Hafnarfjörður as early as 1533. Through German trade connections, many young Icelanders studied in Hamburg.