Knut Eriksson's sons continued to live in the Swedish royal court and were raised by King Sverker.

Erik and his brothers had kin ties with the Norwegian Birkebeiner party since Jarl Håkon Galen was married to their cousin, and sought their support.

In January 1208 Erik nevertheless defeated Sverker in the Battle of Lena and slew the Danish commander Ebbe Sunesen, whose troops suffered great losses.

[4] Popular tradition depicted the event as a battle between Sweden and Denmark where "two Danes ran for one Swede, and their backs were badly spanked by the Swedish men.

This person was the originator of the Folkung party which played a political role in 13th-century Sweden and is frequently confused with the royal family that reigned after 1250.

[8] Sverker and the archbishop Valerius fled to Denmark after the defeat and applied for the intervention of Pope Innocent III.

Innocent ordered the bishops of Skara, Linköping and a third see to persuade Erik to come to terms with Sverker and return the royal prerogatives.

[9] The banner under which King Erik's troops fought, was preserved by his kinsman the lawspeaker Eskil Magnusson of the Bjälbo family in Skara, who in 1219 gave it as honorary to his visiting Icelandic colleague Snorre Sturlasson.

He did not leave a son at his demise, though Queen Rikissa gave birth to a boy named Erik shortly afterwards.