Olaf Haraldssøn Geirstadalf Digerbein (Agder, c. 877 - Tønsberg, c. 934), was a reputed son of King Harald Fairhair of Norway with Svanhild Øysteinsdatter, daughter of Øystein Jarl.
The saga Heimskringla, written in Iceland in the thirteenth century by the poet and historian Snorri Sturluson, gives the ninth century Norwegian founder king Harald Fairhair three sons with Svanhild, including Ragnar Rykkel, Bjørn Farmann and Olaf Haraldsson Geirstadalf.
Olaf Haraldsson was made king of Vingulmark by his father and then later inherited Vestfold after his brother Bjørn Farmann had been killed by their half-brother Eric Blodøks.
The three kings met in battle at the farm Haugar outside Tønsberg, Olaf and Sigrød were defeated and they both fell there.
Today the site is located on the Jarlsberg Estate situated northwest of the centre of the town of Tønsberg.