The Story of Norway by Hjalmar Hjorth Boysen

We have seen that Christianity did not advance in Norway during the mild and lax government of the earls. Olaf Tryggvesson, with all his zeal and vigor, could not in the short space of five years eradicate paganism from the Norsemen's hearts; and after his death a great number of those whom he had compelled to profess the Christian name relapsed into their former practices. It was not until King Olaf Haroldsson by his life, and still more by his death, took the imagination of the Norsemen captive, that Christianity became securely established in the land.

Olaf was the son of Harold Groenske and a grandson of Bjoern the Merchant, who was slain by his brother, Erik Blood-axe. It was accordingly a new branch of the race of Harold the Fairhaired who with him ascended the throne. His father, as we have seen, was burned to death by Sigrid the Haughty, whom he had the presumption to woo, regardless of the fact that he had a wife named Aasta, who was then expecting her confinement. Olaf was born in the house of his maternal grandfather and passed his childhood with Sigurd Syr, king in Ringerike, whom his mother married. Sigurd Syr was a grandson of Sigurd the Giant, a son of Harold the Fairhaired and Snefrid, and had accordingly as much right to the throne as Olaf Tryggvesson, who was then reigning. He was, however, a quiet and unpretentious man, who was contented to raise his crops and superintend his large estates, without troubling himself with ambitious projects.