Niels of Denmark (born circa 1064 - died 1134), was king of Denmark following his brother Eric I. He was presumably the youngest son of king Sweyn Estridson and married Margaret, princess of Sweden, with whom he had prince Magnus .

Four of Niels' older brothers had ascended to the throne before him, and when Eric I "The Evergood" died in July 1103 during a pilgrimage, Niels, or Nikolas as he is sometimes called, was elected King the following year. The exact year of his birth is not known, but he was supposedly born in the mid-1060s, and so was around forty years of age at the time. Niels was king in a time of peace, and the few sources available to us from the early 12th century indicates that he was well-liked by almost everybody, even though some of the more warrior-minded members of his army apparently disagreed with his decision to abandon corporal punishment in favour of a more modern judicial system which relied mainly on fines.

But after 26 years of peace, once Niels' son Magnus had reached adulthood, a conflict erupted between him (Magnus) and his cousin Canute (Knud) Lavard, the son of Eric "Evergood". Canute was very popular in the duchy of Schleswig-Holstein, where he was employed as king Niels' earl, and Magnus (rightly) viewed Canute as a likely contender for the throne once the ageing king passed away. On January 7th, 1131, Magnus slew his cousin near Haraldsted just north of Ringsted, and a civil war ensued as Canute's half-brother Eric tried to avenge his death (and secure the throne for himself in the process).

But the church and seemingly most of the Danish public still supported king Niels, and Eric made little progress, being forced at last to flee to Sweden in 1134. However, when Niels and Magnus landed at Fodevig bay in Scania just before midsummer, determined to finish off Eric once and for all, they were taken by surprise by a contingent of German soldiers on horses, Niels' army were slaughtered before they had time to regroup, and Magnus was slain. King Niels himself escaped alive, but inexplicably chose to travel south to Schleswig where people were as ancious as ever to avenge the slain Canute Lavard, and as Niels arrived in the town of Schleswig on June 25th 1134, the air was shimmering with hatred. The town's priests rushed out to meet him, warning him to seek shelter in the cathedral, but the old king refused the offer: "-Should I fear tinkers and tailors", he supposedly remarked, and started to walk through main street on foot, surrounded only by his personal vanguard.

We don't know what Niels was thinking, although some have suggested that the defeat at Fodevig had broken his spirits, and he was actively seeking his own death. But we do know that as he neared the royal palace, his vanguard was engaged in battle by armed townspeople, and slain one by one as they defended their lord. Finally king Niels himself was felled, and thus ended the reign of the last of Sweyn Estridson's sons. He and his brothers had ruled Denmark for a total of sixty years, and while all of them were remarkable in their own way, Niels was perhaps the best one, a skilled administrator and pragmatician who finished what his father had started and brought Denmark all the way into the Middle Ages.