Magnus I Olafsson, byname Magnus the Good, Norwegian Magnus den Gode, (born 1024, Norway—died Oct. 25, 1047, Skibby, Den.), Norwegian ruler, king of Norway (1035–47) and Denmark (1042–47), who wrested hegemony in the two Scandinavian nations from descendants of Canute the Great (d. 1035), king of Denmark and England.
An illegitimate son of the Norwegian king Olaf II Haraldsson (St. Olaf), Magnus was named after the Holy Roman emperor Charlemagne (Old Norse: Karlamagnús) and was taken to Russia at the age of four with his father, who had been exiled by Canute. In 1035 the chiefs of Norway rebelled against the rule of Canute’s son Sweyn (Svein) and elected Magnus king. As a very young king, Magnus took his revenge on those chiefs who had fought against his father, but later in life he avoided such lawless behaviour, thereby earning the byname of “the Good.”
Canute’s son Hardecanute, who became king of Denmark in 1035 and England in 1040, also claimed the Norwegian throne but later accepted Magnus’s sovereignty, which by then was solidly established. The two rulers agreed that whoever survived would rule both Norway and Denmark.
When Hardecanute died in 1042, Magnus also became king of Denmark and appointed as his viceroy Canute’s nephew Sweyn (Svein) Estridsson (later Sweyn II). Sweyn, however, soon challenged Magnus’s sovereignty in Denmark. Magnus received the support of most Danes, who needed his help against the Wends (Slavs) in southern Jutland, and he repeatedly defeated Sweyn in battle. After Magnus’s uncle Harald III Sigurdsson returned from Constantinople (now Istanbul) in 1045, the two men agreed to share the kingdom. Magnus died in a campaign launched by the co-rulers against Denmark in 1047, aborting his plans to claim the English throne.