Horik I or Hårik (died 854) was a king of the Danes. He was co-ruler from 813, and sole king from c. 828 until his violent death in 854. His long and eventful reign was marked by Danish raids on the Carolingian Empire of Louis the Pious, son and successor of Charlemagne.
Background
Horik's father was King Gudfred, known for his successful raids and wars against Charlemagne's Frankish empire and against the Obodrites. If the later author Notker of Saint Gall can be trusted, his mother may have been disowned by Gudfred in the early 9th century. In 810, Gudfred was assassinated by a housecarl, or, in Notker's version, by one of his sons as revenge for the treatment of his mother. His nephew Hemming succeeded him. Gudfred had at least five sons. It is unknown why kingship descended on a side-branch of the dynasty, though Hemming was possibly older than his cousins. The new king made peace with Charlemagne in 811.
Hemming's reign as king was short-lived and he died in 812. After his demise, a violent civil war broke out. Another dynastic branch, Harald Klak and Ragnfred, gained power during the conflict. The party of the five sons of Gudfred, of whom only Horik is known by name, sought refuge with the Swedes during the unrest. Harald and Ragnfred entertained good relations with Charlemagne.
Becoming king
Harald and Ragnfred were busy fighting rebels in Vestfold in Norway, the farthest part of their realm. After their return to Denmark in 813, they were attacked by Gudred's sons and their noble retainers, who had returned from Sweden. The five brothers found support from all over the Danish realm, defeated Harald and Ragnfred with relative ease, and expelled them from Denmark. In that way the brothers were elevated as Danish co-rulers. Whether they split the realm into parts or ruled collectively is not known. In the next year, Harald and Ragnfred gathered a force and attacked their rivals. A battle was fought where Ragnfred and the oldest son of Gudfred were both slain. However, the remaining four brothers gained victory. Harald acknowledged defeat and fled to the new Frankish Emperor Louis the Pious who had just succeeded his father Charlemagne. Louis ordered him to stay in Saxony and await the right occasion when the Franks would be able to help him regain his throne.
During the winter, Louis ordered the Saxons and Obodrites to prepare for the invasion of Denmark. In May 815 the troops moved northward over the Elbe and reached Sinlendi (in South Jutland). Then they marched for seven days until they reached a shore, three miles from a certain island (possibly Funen). The four brother kings had gathered a fleet of 200 ships and were posted on the island, refusing to offer the imperial troops battle. The imperial envoy Baldrich let his troops ravage the districts in the neighbourhood, took 40 hostages, and returned without having achieved much.
Ex-king Harald did not give up and repeatedly raided the realm of Gudfred's sons from his base in the Frankish Empire. In 817 the sons asked Emperor Louis to make peace in order to halt the attacks. However, the Frankish court considered this mere hypocrisy. On the contrary, Louis continued to support Harald's cause. Next, the Obodrite ruler Slavomir, a vassal of Louis, defected since the emperor forced him to share power with another prince, Keadrag. Instead, Slavomir sent a message to Gudfred's sons and suggested an alliance. In fact, a Danish Viking fleet sailed up the Elbe and laid waste to the Stör area. The Danish border chief Glum attacked the Frankish fortress Esesfeld with a force of Danes and Obodrites, but had to withdraw in the face of spirited Frankish resistance.