Halfdan (flourished 9th century) was the founder of the Danish kingdom of York (875/876), supposedly the son of Ragnar Lothbrok, the most famous Viking of the 9th century.
After participating in raids on Anglo-Saxon lands to the south, Halfdan and his followers invaded the mouth of the River Tyne (874) and engaged in warfare with both Picts and the Britons of Strathclyde. In 876 he distributed the large region of York among his men and may then have left to join Viking campaigns in northern Ireland; he may be the Danish king “Albann” who was slain near Strangford Lough in 877. By another account he remained in York until 883.