Question: Hagbard and Signe was based on characters from a work by which Danish historian?

Context paragraphs:
Torben Jørgensen: Torben Jørgensen (born 1958) is a Danish historian, Research Assistant at the Danish Center for Holocaust and Genocide Studies.  He is an author of articles on the Hereros and the Ibos (Encyclopedia of Genocide, 2000) and about the Turkish denial of the Armenian genocide ("Historisk Tidsskrift", 2000).  He participated on a project on those responsible for running the death camps Belzec, Sobibór and Treblinka.

Jakob Langebek: Jakob Langebek (23 January 1710 - 16 August 1775) was a Danish historian

Hagbard and Signe: Hagbard and Signe or The Red Mantle (Danish: "Den røde kappe" , Swedish: "Den röda kappan" , Icelandic: "Rauðu skikkjuna" ) is a 1967 Danish-Swedish-Icelandic drama film based on the story of Hagbard and Signy from the twelfth-century work "Gesta Danorum" by Saxo Grammaticus, directed by Gabriel Axel and starring Gitte Hænning.  The film won a Technical Prize ("Mention spéciale du grand prix technique") at the 1967 Cannes Film Festival.

Aage Friis: Aage Friis (16 August 1870, Korsør, Denmark – 5 October 1949, Hellerup) was a Danish historian and university lecturer.

Tom Buk-Swienty: Tom Buk-Swienty (born July 19, 1966 in Eutin) is a Danish historian, journalist and author, known for his work on the Second Schleswig War.

Kristian Erslev: Kristian Sophus August Erslev (December 28, 1852, Copenhagen – June 20, 1930, Frederiksberg) was a Danish historian.  His work involved a variety of subjects, including Historiography.  Erslev's influence on the Danish academic community was great and he was considered "the master" Danish historian.  As editor of the Danish "Historisk Tidsskrift" he also set the standards for solid, factual historical writing.  He looked to other European scientists for inspiration, but never fully solved the problems of objectivity and the influence of "the person behind the pen".  He was openly attacked by later generations of Danish historians for his strong belief in "the truth".

Saxo Grammaticus: Saxo Grammaticus ( 1150 – c. 1220), also known as Saxo cognomine Longus, was a Danish historian, theologian and author.  He is thought to have been a clerk or secretary to Absalon, Archbishop of Lund, the main advisor to Valdemar I of Denmark.  He is the author of the first full history of Denmark.

Hagbard and Signy: Hagbard and Signe (Signy) (the Viking Age) or Habor and Sign(h)ild (the Middle Ages and later) were a pair of lovers in Scandinavian mythology and folklore whose legend was widely popular.  The heroes' connections with other legendary characters place the events in the 5th century AD.  Hagbard and his brother Haki were famous sea-kings (see Haki for his battles over the throne of Sweden).  Like the name Hagbard ("Hagbarðr"), the legend is believed to have continental Germanic origins.

Kåre Johannessen: Kåre Johannessen (born 1964) is a Danish historian, writer, lecturer and presenter.  He is the former curator at the museum of Trelleborg and Middelaldercentret, where he worked from 1994–1999 and again from 2004–2015.  Today he is a self-employed historian.  While working at Trelleborg he recreated the Viking game of knattleikr and injured his knee so badly that he had to use crutches for a time.

Peter Rochegune Munch: Peter Rochegune Munch (in Danish usually referred to as "P. Munch") (1870–1948) was a leading Danish historian and politician.  He was a leading member of the "Radikale Venstre", and represented Langeland in parliament.

Supporting paragraphs: Hagbard and Signe Saxo Grammaticus
Answer: Saxo Grammaticus