Sigfred was possibly the second official king of Denmark

Denmark

Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

 whose reign started no later than the 770s and ended around 800. The precise dates remains unknown.
He was most likely the father of Gudfred

Gudfred

King Gudfred was a Danish king during the Viking era. Gudfred was the younger son of King Sigfred. Alternate spelling include Godfred, Göttrick , Gøtrik , Gudrød , and Godofredus .-Biography:King Gudfred appeared in present day Holstein with a navy in 804 AD where diplomacy took place with the...

, who later reigned as king of Denmark. It has been theorized that his father was Ongendus

Ongendus

Ongendus was a king of the Danes, reigning c. 710.About 710, Saint Willibrord visited the Danes whilst Ongendus was ruling and returned with 30 boys to instruct in missionary work. No further details are given about Ongendus, other than that he was "more savage than any beast and harder than...

, or Angantyr, generally believed to have been the first king of Denmark.