Haakon VI of Norway

Haakon Magnusson became King of Norway in 1343 as a child, the younger son of Magnus Eriksson who ruled both Norway and Sweden. Magnus's obvious favoritism drove Haakon's older brother Eric to rebellion and the seizure of Southern Sweden; when Eric died in 1359, Haakon stepped into the Swedish succession as his father's co-ruler three years later. That joint reign lasted only until 1364, when exiled Swedish nobles led by Bo Jonsson Grip installed Albert of Mecklenburg and pushed both father and son out - efforts to retake Sweden failed. His 1363 marriage to Margaret of Denmark dragged him into continuous conflict with her father Valdemar IV until the Danish king's death in 1375, at which point Haakon maneuvered his son Olav onto the Danish throne ahead of Mecklenburg rivals. When Haakon died in 1380, Olav inherited Norway and Denmark with Margaret as regent; seven years later the boy died childless, and Margaret became the first woman to rule all three Scandinavian kingdoms outright.