Olaf II Haraldsson (c. 995 – 29 July 1030), later known as Saint Olaf (and traditionally as St. Olave), was King of Norway from 1015 to 1028. Son of Harald Grenske, a petty king in Vestfold, Norway, he was posthumously given the title Rex Perpetuus Norvegiae (English: Eternal/Perpetual King of Norway) and canonised at Nidaros (Trondheim) by Bishop Grimkell, one year after his death in the Battle of Stiklestad on 29 July 1030. His remains were enshrined in Nidaros Cathedral, built over his burial site. His sainthood encouraged the widespread adoption of Christianity by Scandinavia's Vikings/Norsemen.

Pope Alexander III confirmed Olaf's local canonisation in 1164, making him a universally recognised saint of the Roman Catholic Church and started to be known as Rex Perpetuus Norvegiae - eternal king of Norway. He became an equally important saint of the Eastern Orthodox Church (feast day 29 July) and one of the last famous saints before the Great Schism. Following the Reformation he was a commemorated historical figure among some members of the Lutheran and Anglican Communions.The saga of Olav Haraldsson and the legend of Olaf the Saint became central to a national identity. Especially during the period of romantic nationalism, Olaf was a symbol of Norwegian independence and pride. Saint Olaf is symbolised by the axe in Norway's coat of arms and Olsok (29 July) is still his day of celebration. Many Christian institutions with Scandinavian links as well as Norway's Order of St. Olav are named after him.