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In page List of monarchs of Norway:

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The Danish king Harald Bluetooth had himself hailed as king of Norway after the Battle of Fitjar (c. 961). Besides gaining direct control of Viken in south-eastern Norway, he let Harald Greycloak rule the rest of Norway as king, nominally under himself.[citation needed] Harald Bluetooth later switched his support to Harald Greycloak's rival, Haakon Sigurdsson, Earl of Lade, who eventually captured Harald Greycloak's kingdom. Haakon thereafter ruled Norway (except Viken), at first nominally under Harald. All dates are estimates and subject to interpretation.[1] Haakon is generally held as the ruler of Norway from 970 to 995.[2]