Margrethe 1 (1353-1412) was the daughter of the Danish King Valdemar Atterdag. When she was about 10 years old she was married to the Norwegian King Håkon and in 1370 Margrethe gave birth to a boy, Oluf. When Valdemar Atterdag died there was no heir apparent to the Danish throne so it passed to Margrethe's five-year old son, Oluf, and the government was left to his parents as regents. Håkon died in 1380, so Oluf inherited to Norwegian throne as well. But since he was still only ten, Margrethe now ruled Denmark and Norway. When Oluf died at just 17, Margrethe was given the title of "Supreme mistress over the Kingdom of Denmark" - somethin similar had never been seen before. She also took over the Swedish and Norwegian throne after a revolt against an unpopular Swedish King. She tried to bring order to her countries through laws that diminished the power of the Nobility and with the Kalmar Union in 1397 Denmark, Norway and Sweden was united under one monarchy, but each country kept their individual laws. Margrethe adopted Erik of Pommern, who was also from royal birth, and made him her heir. She ruled independently until she died of the plague in 1412.