Harald was the youngest of King Olaf II of Norway

It is a fact that Harald was the youngest of King Olaf II of Norway. Harald was born in 1015 (or maybe 1016) in Ringerike, Norway to Sta Gudbrandsdatter and her second husband Sigurd Syr. Sigurd was a Ringerike minor king and one of the strongest and wealthiest chieftains in the Uplands. Harald was the youngest of King Olaf II of Norway's three half-brothers by his mother sta (Olaf II Haraldsson, later known as Saint Olaf (and traditionally as St. Olave), was King of Norway from 1015 to 1028). Harald was a typical rebel with huge dreams in his childhood, and he looked up to Olaf as a role model. He so contrasted with his two elder brothers, who were more like their father, down-to-earth, and mostly concerned with farm maintenance.

The Icelandic sagas, particularly Snorri Sturluson's Heimskringla, suggest that Sigurd, like Olaf's father, was a male-line great-grandson of King Harald Fairhair. Most current academics believe that the forebears assigned to Harald Hardrada's father, as well as other elements of the Fairhair genealogy, are inventions reflecting the authors' political and social ambitions rather than historical truth. Harald Hardrada's supposed lineage from Harald Fairhair is never stated or played any role during his lifetime, which is odd given that it would have supplied important legitimacy in conjunction with his claim to the Norwegian crown.