I'm not a historian but for any Norwegian it's an important part of our general education; Norway was (forcefully) converted to Christianity in large parts by two consecutive kings; King Olav I and Olav II. King Olav II "the Holy" was made a saint by the catholic church so the proper way to address him is Saint Olav as a sainthood takes presidency over a noble title. The christianization of Norway was started by the King before him - King Olav I Trygvasson who also founded the city of Trondheim.

I'm fully expecting my post to be deleted but hopefully it will spur on some actual historians to make a better post.

Quite a broad question but as a sort of background:

The Christianisation of Norway is quite difficult to nail down in terms of detail as contemporary sources aren't exactly abundant and later documents aren't considered wholly reliable. It's been speculated for example that many of the sagas surrounding this event were told in such a way as to present the Christianisation as being something very abrupt and violent for dramatic purposes - whereas there is archaeological evidence of Christian symbols found in Norway that can be dated back to the 8th century, showing that at least in some areas, conversion was very gradual.

There is also the problem with Viking communities of the time being very fragmented and this went down to their beliefs as well. There have been studies of Norse grave sites done across the country with a big variance in what religious symbols people were buried with (highlighting their specific adherence, some being members of Tors Cult for example, others being Christian). Annoyingly, a chronology is hard to nail down because radiocarbon testing isn't as precise as we would like it to be.

What we do know for sure is that the first Kings of Norway, King Olav Tryggvason and King Olav Haraldsson, were very eager to promote Christianity. Both were raised outside Norway by Christian rulers and both wanted to use Christianity as a means to promote hierarchical power within Norway for ideological reasons. With this in mind they both founded several towns to act as 'beacons of light' that, as they grew, would help spread the faith among the common people. It's worth noting though, that as Christian symbols have been discovered in Norway prior to the arrival of the 'missionary kings', there were also pre-existing Christian towns, Véøy is a good example. Likewise, old Viking towns like Kaupang contain no Christian burial sites at all, this is despite decades of excavations. This town existed well into the 10th century so we know for sure that some tried to resist the Christians.

Sources:

Bagge, S. 2005. Christianization and State Formation in early Medieval Norway

Nordeide, S. W. 2006. Thor's hammer in Norway. A symbol of reaction against the Christian cross?

The second source is really interesting and goes into the study of grave sites in a lot of detail.

FYI, you'll find a few posts on the general topic of Norse conversion in the FAQ (link on sidebar):

The Norse and the Vikings