Olav Haraldsson is the
sainted Norwegian King that has been credited for
christening Norway. Large parts of Norway had in fact already turned to
Christianity at the time Olav became king (1015), especially along the coast (where presumably foreign influence were biggest). Nonetheless, Olav travelled around Norway and made sure that the people knew who to
worship. Probably, a lot of
politics were involved, it may have been more a matter of showing who the king was than religion.
Olav established the Catholic Church in Norway by bringing four bishops to the country from England. A law was made denouncing the old gods, and introducing Christian holidays, prohibition against polygamy and other Christian values. This was the beginning of an escalating conflict with local power around Norway. In addition to the religious affairs, Olav wanted a kingdom much like Carl the Great's, where a just and rightous king would have total power.
The outbreak happened when king Knut (Canute) of Denmark and England announced a claim to Norway. He was rich and powerful, and bribed powerful men in Norway to join him against Olav. As Knut invades with local support, Olav must flee to Sweden, and further to Novograd in Gardarike (Russia). He gathers a small army and returns to Norway, where he fights his last battle at Stiklestad against bad odds in 1030. He was, according to Snorre Sturlasson's sagas, killed with a spear by Tore Hund.
Tore Hund was the first person to declare Olavs holiness. Many of Olav's former enemies regretted their opposition against what they now saw as a fair and holy king. This may be explained by the fact that the new king, Knut's son Svein, made even stricter laws than Olav. Olav was declared a saint and removed from his grave. According to tradition, his hair and nails had grown in the months after the battle.
See Monarchs of Norway for a list of Norwegian rulers.
Source: The Norwegian Catholic Church, www.katolsk.no
Update July 17, 2002:
As an interesting aside: I just read on snopes, a myth debunking site, that a human body (and in particular the skin) shrinks after death, creating the illusion that hair and nails have grown. This effect seems to be known by funeral agents, who will sometimes moisturise their clients to avoid the effect.