Ulf the Earl
Ulf (or Ulf Jarl) (Ulf Thorgilsson) was a Danish earl (jarl) and regent of Denmark. Ulf was the father of King Sweyn II of Denmark and thus the progenitor of the House of Estridsen, which would rule Denmark from 1047 to 1375, which was also sometimes, specially in Swedish sources, referred to as the Ulfinger dynasty to honor him. 
Ulf Jarl was the son of Thorgils Sprakalägg. His brother was Eilaf, an earl of King Cnut the Great, and his sister was Gytha Thorkelsdóttir who married Godwin, Earl of Wessex. He participated in Cnut the Great's conquest of England as one of his most trusted men. In 1015-16, he married Cnut's sister, Estrid Svendsdatter of Denmark, who gave birth to their son, Svein, who later became the king of Denmark. From c. 1024 he was appointed the Jarl of Denmark and King Cnut's appointee as regent of Denmark, which he ruled when the king was absent. He was also the foster-father and guardian of King Cnut's son Harthacnut.
In 1026, the Swedish king Anund Jakob and the Norwegian king Olaf II took advantage of King Cnut's absence and launched an attack on the Danish in the Baltic Sea. Ulf convinced the freemen to elect Harthacnut king, since they were discontented at Cnut's absenteeism. This was a ruse on Ulf's part since his role as Harthacnut's guardian would make him the ruler of Denmark.
When Cnut learnt what had happened, he returned to Denmark and with Earl Ulf's help, defeated the Swedes and the Norwegians at the Battle of the Helgeå. However, Ulf's assistance did not cause Cnut to forgive him for his own role in the coup. At a banquet in Roskilde, the two brothers-in-law were playing chess and started arguing with each other. The next day, the Christmas of 1026, Cnut had one of his housecarls kill Earl Ulf in Trinity Church, the predecessor of Roskilde Cathedral. However, accounts contradict each other.
- "Ulf Jarl". Gyldendal. Retrieved 2010-01-22.
- Heimskringla (1964 ed.). University of Texas Press. p. 408. ISBN 0292730616.
- M. K. Lawson, Cnut: England's Viking King (2004), p. 94, says that the identification of Ulf with the husband of Estrith (Estrid) is commonly made but not certain.
- Ulf Jarl (Nordisk familjebok. 1920)
- Havhingsten fra Glendalough: The battle of the throne of England