Halfdan Ragnarsson is the younger brother of Ivarr and Ubba. He appears in Bernard Cornwell's The Last Kingdom, though he has not appeared in the BBC adaptation.
Halfdan arrived in England about a year or so after his brothers and briefly led what he called the "Great Danish Army" (the 'Great Heathen Army') and occupied Lundenberg (modern London) for a time, while Ivar and Ubba went to campaign in Ireland.
Halfdan was boisterous and aggressive, but he lacked the strategic foresight of Ivarr and the sheer ferocity of Ubba. The Great Danish Army struggled in its conflict with the Kingdom of Wessex under Halfdan's command.
- Some historians have contended that Halfdan, named in the Anglo-Saxon Chronicle, is the same person as Hvitserk from the Snorri Sturlusson's Saga of Ragnar Lothbrok. The latter tale, however, states that Hvitserk died while campaigning in Russia.