Ancestry and Background
Little is recorded about Thorgil in historic text. Most of what was recorded is in reference to his children, two of whom were parents of royalty. Thorgil's cognomen Sprakalägg translated in English means Strut-leg. In the Icelandic Knýtlinga saga he is also called "the fast". In the 11th-century, English historian Florence of Worcester named his father as 'Ursius' (i.e. urso, Latin for bear or Bjørn in Danish, Björn in Swedish). 
In the 13th-century, Danish historian Saxo Grammaticus records the folklore that Ursius/Björn was the son of a bear and a fair Swedish maiden. Genealogical speculations of a later date (presumably first suggested by the Danish historians Jakob Langebek and Peter Frederik Suhm) would make Thorgil the son of Swedish warrior Styrbjörn the Strong (Styrbjörn Starke), who in turn was depicted as having been a son of Olaf Björnsson, king of Sweden.
Styrbjorn's wife in the sagas is stated to have been Tyra of Denmark, the daughter of Harold Bluetooth, king of Denmark and Norway. No primary source supports this theory about Thorgil's royal ancestry and the theory itself is almost impossible to maintain because of the chronological inconsistencies. About Thorgil's death, it can only do fairly safely believed that he died circa 1009.
- Ulf (died 1027) - Earl in Denmark and brother-in law of King Cnut the Great. His son became King Sweyn II of Denmark.
- Eilaf (first mentioned 1009) - Earl of King Canute.
- Gytha Thorkelsdóttir - married Godwin, Earl of Wessex. mother of King Harold Godwinson of England and Edith of Wessex, Queen of King Edward the Confessor
- Lawætz, Peter "Danske vikingekonger – én slægt med mange grene" April 2011
- Lawætz, Peter (April 2011). "Ulf jarls herkomst". vikingekonger.dk. Retrieved April 1, 2016.
- Arthur, Ross G. "Bjorn - Bear" (PDF). English-Old Norse Dictionary. Retrieved April 1, 2016.
- Searle, W.G. (1899) archive.org Anglo-Saxon Bishops, Kings, and Nobles: The Succession of the Bishops and the Pedigrees of the Kings and Nobles (London: Cambridge University Press. pp.355).
- "Styrbjörn Starke". Nordisk familjebok. 1918. Retrieved April 1, 2016.
- "Ulf". Dansk Biografisk Leksikon. Retrieved April 1, 2016.
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