Sweyn II of Denmark
The mother of Magnus was Ingrid Ragvaldsdotter, a granddaughter of King Inge I of Sweden. His father was the Danish lord Henrik Skatelår, son of an illegitimate son of king Sweyn II of Denmark. After Henrik's death, Ingrid remarried thrice, with Harald Gille of Norway, then Ottar Birting, and finally Arne from Stårheim. Magnus therefore had kinship ties with the royalty of the three Nordic kingdoms. He was married to his stepsister Bridget Haraldsdotter, a daughter of Harald Gille who had previously been married to the powerful jarl in Västergötland, Karl Sunesson. Magnus is first mentioned in 1148 when he witnessed a document issued by King Sweyn III of Denmark.