For 10 points, name this royal position held by Charles XII and Gustavus, who ruled a kingdom from Stockholm.
The first Christian man to hold this position had the name Skotkonung and was baptized at Husaby. The man in this office during the Black Plague clashed with St. Birgitta. This position was held by a man who won the Battle of Narva before a disastrous defeat at Poltava the Great Northern War. This position was subsumed by the Kalmar Union with Denmark and Norway until the House of Vasa emerged and took this position. For 10 points, name this royal position held by Charles XII and Gustavus, who ruled a kingdom from Stockholm.
The first Christian man to hold this position had the name Skotkonung and was baptized at Husaby.
King of Sweden [accept Ruler of Sweden or equivalents involving Sweden]