|King of Viken|
|Reign||14th September, 1099 - 4th June, 1137|
|Predecessor||Cnut II (IV)|
|Spouse|| Margaret Fredskolla|
|Issue|| Inge Nielsen|
|House||House of Estridsson|
|Father||Sweyn II Estridsson|
|Born|| c. 1065 |
|Died|| 4th June, 1137 |
Niels I, sometimes regarded as the youngest legitimate son of Sweyn II of Denmark, inherited Viken after the death of his brother Cnut II (IV) in 1099. His reign was marked by an increased level of antipathy and violence between the Scandinavian states.
Possibly sent to Flanders in 1086 as a hostage Niels appears to have much of his early years as a lord in Viken where he had garnered the reputation for being fair and with an interest in reforming various archaic practices especially when it came to taxation and raising armies. As king he also led his nobility out on raids into Wendland in conjunction with Poland.
At first Niels and his elder brother Eric I split Cnut IV's realms peacefully however their relationship soon turned sour. When Eric died on a pilgrimage to the Holy Land in 1103 Niels took the opportunity to invade Denmark. However Eric's son Harald IV Kesja had anticipated the attack and would prove victorious. At the Flemish court later in the year the three Estridsson kingdoms (Viken, Denmark and Anglia) pledged friendship. As long as a legitimate Estridsson ruled then they promised not to invade each other.
Blocked from extending his rule over Denmark, Niels attempted to build his own dynastical legacy instead. His marriage to Margaret Fredskolla, daughter of Inge I of Svealand produced one son, Magnus, now in line to inherit both kingdoms. Magnus I duly inherited Svealand after the death of Inge II in 1125. However his rule was marred by revolt and he ousted in 1130 by Svealand's nobles who elected Sverker of Gothenland in his place. Even worse, Niels' wife, Ulvhild, previously married to Inge II, ran away to become Sverker's new wife. With the resources of Gothenland and Svealand arrayed against him (and with Denmark busying itself in other ways) Niels could do little but shore up his defenses. All out war was avoided but it marred Niels' good reputation.
Margaret Fredskolla had proved a formidable queen and her absence was sorely missed by Viken. She appears to have done more ruling than Niels ever attempted, was diplomatically able and even had coins minted with her name on them. The period after her death 1130-1137 was marked by a increasingly restive nobility and it seems as though Niels handed most of his direct power to his son Magnus by 1132. He would die in 1137.