Sweyn II of Denmark (The Kalmar Union)

Sweyn II was the first Danish monarch of the Estridsson dynasty. His massive family helped extend Estridsson control and influence over much of Denmark's neighbours and direct control of Viken, Denmark and Gothenland would help stabilise relations in Scandinavia and ensure a familial connection between the states leading towards the first Kalmar Union.

Born in Norfolk in 1019 during his uncle Cnut I's reign in Anglia, Sweyn travelled to Denmark with his father and mother after Cnut successfully gained its throne later that year. Cnut's youngest son Harthacnut was installed as Denmark's regent, under the guidance of Sweyn's parents; Ulf, Jarl of Orkney and Estrid Svendsdatter, Cnut's sister. Sweyn made sure to use the matronymic Estridsson rather than Ulfsson to emphasize the link back to the older Danish kings. Sweyn was friendly with his cousin and Harthacnut gave him an earldom in return for military service, but he also campaigned on behalf of the Svealandic king Anund Kolbranna.

After Harthacnut lost Denmark to Magnus I of Hordaland (who had already conquered Viken from Sveinn I Knutsson) Sweyn briefly was employed by him as Jarl of Jutland. But ambition meant he soon took up the war against him. Sweyn appears to have held Scania in defiance of Magnus' forces but could not find victory elsewhere in Denmark. In 1047 however Magnus died, leaving Denmark and Viken to Sweyn and the Hordaland to his son Harald IV Hardrada. A long feud with Harald began as Harald refused to give up his claims to the other kingdoms and Sweyn often found himself on the backfoot. Harald eventually came to terms with Sweyn and they acknowledged each other's claims to their respective thrones. Harald then attempted to resurrect Magnus's claims to Anglia (as Harthacnut regarded Harald I Harefoot as a usurper so did Magnus) and would lose his life attempting to seize Jorvik.

Despite some of his lord's wishes he sent messages of good will to his cousin Harald I in Anglia, swearing off the conquest of Anglia as both Harthacnut and Harald Hardrada had previously attempted. Instead he sought to consolidate his power at home by increasing Danish power over their own church. Previously filled with German priests looking to Hamburg-Bremen, Sweyn managed to replace them slowly with Anglians and donated large tracts of land to establish the dioceses' independence. An avid church builder, he became good friends with Pope Gregory VII, meaning he could bypass Bremen and negotiate directly for the Danish church's increased status.

He campaigned repeatedly on behalf of others, helping Emperor Henry III pacify the Low Countries and interfering in the civil wars of the Polabian Lutici.

On his death in 1047 Sweyn II's three kingdoms were divided between the three oldest surviving sons; Viken went to Cnut IV, Denmark to Harald III Hen and Gothenland to Olaf I Hunger. Two other sons; Eric and Niels would become kings in due course. He took endless mistresses and would have 20 children overall.