The saga Ragnarssona þáttr relates the acts of the sons of Ragnar Lodbrok, and proceeds to link them genealogically to the later rulers of the Scandinavian kingdoms.

That Sigtrygg was the son of Gnupa by a Danish noblewoman named Asfrid, and is shown on two runestones near Schleswig, erected by his mother after his death.

[2] Adam then relates that after Sigtrygg reigned a short time, during the tenure of Archbishop Hoger of Bremen (909–915/917), Hardegon, son of Sweyn, came from "Northmannia" the "land of the Northmen," by which he may have meant Norway, Northumbria, Normandy, which had recently been colonized by Danish Vikings, or even northern Jutland.

The Saxon chronicles of Widukind of Corvey report the defeat and forced baptism of the Danish king Chnuba (Gnupa), in 934 at the hands of Henry I.

[5] Some historians (e.g. Storm) have taken these as indications that Sigtrygg's father Gnupa still ruled at least part of Denmark much later than credited by Adam of Bremen, and his dynasty was only displaced by Harthacnut's son, Gorm.

[6] In the Silverdale Hoard is a silver coin impressed with the name "Airdeconut" an Anglicized[citation needed] or Romanized[7] variant of Harthacnut.