Horik I (died 854) reigned as sole King of the Danes from 827 to his violent death in 854. His reign was marked by Danish raids on the Franco-German empire of Louis the Pious, son and successor of Charlemagne.
Horik's father was King Gudfred, known for his successful raids and wars against Charlemagne's Frankish empire and against the Abodrites. In 810, Gudfred was assassinated by one of his own sons, and his nephew and successor Hemming made peace with Charlemagne.
Hemming did not last long. Horik and another of Gudfred's sons took power in 811, later expelling a rival named Harald Klak, who took refuge at the court of Charlemagne's son and successor, Louis the Pious. In 819, Louis forced Gudfred's sons to accept Harald as co-ruler. Harald converted to Christianity in 826, with Louis standing as his godfather, but Harald was driven out of Denmark for the second and final time one year later. By then Horik was the only son of Gudfred's still alive, making him the sole king of the Danes.
Horik refused to convert to Christianity, as it was his enemies' religion, and resisted attempts by Archbishop Anskar of Hamburg-Bremen to proselytize the Danes. In 845, Horik's army attacked Hamburg and destroyed St. Mary's Cathedral there. It was Horik's last major war in East Francia.
However, Danish raids against Frisia continued. The Franks lacked an effective fleet, so the Danes could raid more or less with impunity. The Danes sacked the silver minting center of Dorestad in 834, 835, and 836, and plundered Walcheren in 837.
King Horik seems to have disapproved of these raids, for successful raiders constituted possible rivals. Occasionally, Horik even punished raiders. In 836, Horik sent an emissary to King Louis declaring that he had nothing to do with the raids on Frisia, and that he had executed those responsible.
In 854, King Horik I was killed by a nephew whom he had driven into exile. While in exile, the nephew had become a successful raider.