Eric XII of Sweden

Erik was born in early 1339 as the eldest son of King Magnus Eriksson (1316–1374) who ruled both Sweden and Norway.^[1] When Magnus' second son, Haakon, was born the following year, Magnus decided to divide the kingdoms between his sons. Erik was designated to succeed his father as King of Sweden, while Haakon would become King of Norway during his father's lifetime.^[1] Although, by Norwegian law, Erik was the rightful heir to the Norwegian throne, the Norwegian Council of the Realm agreed to this arrangement in 1343. In 6 December 1344, Erik was formally elected King of Sweden at the Stones of Mora.^[1]

In 1342, Magnus' brother-in-law, Duke Albrecht of Mecklenburg, approached Holy Roman Emperor Louis IV to propose a union between Erik and Beatrix, the daughter of Louis IV's eldest son, Louis V of Brandenburg, and his first wife, Margrete, daughter of King Christopher II of Denmark. The marriage aligned with Magnus' strategic interests, as Beatrix's dynastic claims could strengthen his position in the ongoing conflicts with King Valdemar Atterdag of Denmark. Additionally, the union could also advance Magnus' ambitions in Estonia, which Valdemar had nominally ceded to Louis as compensation for Margrete's unpaid dowry. However, both Emperor Louis IV and Louis V of Brandenburg had been excommunicated by the Catholic Church, and Magnus had to petition Pope Clement VI regarding the marriage arrangement, as noted in a letter from the pope to the king in 1347.^[1]

The exact date of the wedding is unknown. Beatrix is believed to have been around the same age as Erik, and one of Saint Birgitta's revelations indicates that the marriage took place while she was still a minor. Some sources suggest that the wedding occurred as early as 1346, but the only certainty is that it took place before 25 October 1356.^[1]

In 1355, Haakon was declared of age, and after that, he was the sovereign ruler of Norway, although his father's influence remained significant.^[2] In contrast, Erik held no power while his father continued to reign as King of Sweden.

In 1357, a Swedish rebellion forced King Magnus to share the rule of Sweden with his son Erik, who was allowed domain over most of Scania and Finland. Joint rule of Sweden was established again in 1359 when father and son became reconciled and co-ruled Sweden until Eric's death a few months later. Quite soon after his death his wife, Beatrix, died as well. It is generally believed that they both died of the Black Death.