question: Halfdan Ragnarsson was a commander of a coalition of Norse warriors, originating from where?
answer: Denmark
context: Title: Great Heathen Army
  Passage: The Great Viking Army or Great Danish Army, known by the Anglo-Saxons as the Great Heathen Army (OE: "mycel hæþen here"), was a coalition of Norse warriors, originating from Denmark (and likely also from Sweden and Norway) who came together under a unified command to invade the four Anglo-Saxon kingdoms that constituted England in AD 865.
  Title: Ivar the Boneless
  Passage: Ivar the Boneless (Old Norse: "Ívarr hinn Beinlausi" ; ) was a Viking leader and a commander who invaded what is now England.  According to the "Tale of Ragnar Lodbrok", he was the son of Ragnar Lodbrok and Aslaug.  His brothers included Björn Ironside, Halfdan Ragnarsson, Hvitserk, Sigurd Snake-in-the-Eye and Ubba.
  Title: Halfdan Ragnarsson
  Passage: Halfdan Ragnarsson (Old Norse: "Hálfdan" ; or "Healfdene"; Old Irish: "Albann" ; died 877) was a Viking leader and a commander of the Great Heathen Army which invaded the Anglo-Saxon kingdoms of England, starting in 865.  According to the tradition recorded in the Norse sagas he was one of the sons of Ragnar Lodbrok, and his brothers included Björn Ironside, Ivar the Boneless, Sigurd Snake-in-the-Eye and Ubba.  He was the first Viking King of Northumbria and a pretender to the throne of Kingdom of Dublin.  He died at the Battle of Strangford Lough in 877 trying to press his Irish claim.
  Title: Hvitserk
  Passage: Hvitserk ("Hvitsärk") "White-Shirt" was one of the sons of the legendary 9th-century Norsemen Ragnar Lothbrok and his wife Aslaug.  He is attested to by the Tale of Ragnar's Sons ("Ragnarssona þáttr").  He is not mentioned in any source which mentions Halfdan Ragnarsson, one of the leaders of the Great Heathen Army which invaded the Kingdom of East Anglia in 865, or vice versa which consequently led some scholars to suggest that they are the same individual with "Hvitserk" being only a nickname.
citations: Halfdan Ragnarsson Great Heathen Army