Olaf was a Norwegian lord. After joining Cnut in his conquest of England, Olaf returned home and declared himself king. Sadly not everyone agreed, and most of his reign was disrupted by rebellions and civil war. Nevertheless he continued to spread Christianity throughout Norway. Eventually he was killed in battle against his former ally, and fellow Christian, Cnut. In death, his followers emphasised the evangelical work, and deemphasised the whole viking-theft-of-entire-kingdoms part of his career, to the extent that as patron saint he was able to do what he was unable to do in life - unify Norway.
Fall of Olaf II, Battle of Stiklestad
Olaf was a Norse warlord. As such there's two likely costumes; firstly we can go as strictly historical as we can. Or of course, there's horned helmet, fur trimmed leather jerkin open to the waist, beard, braids and a dragonship. Also a halo.
 Olaf has previously appeared on Night of the Hats in this post.
 Canute in English. Canute continues to be ignored in popular history. A pretty good Time Team special about Vikings was on recently, but the timeline went something like Danish Great Army (860s), Alfred the Great and the Danelaw (870-890s), Danish York (900s)... Harald Hardrada (1066)! "Are you going to completely ignore Canute, Tony?" I asked the TV. He just grinned and told us that Viking meant Pirate. I may need to post on Canute sometime.