Discovering the Barbaric Archipelago
As mentioned in How to Twist a Dragon's Tale, according to Viking legend, Great Hairybottom was sailing and lost his boot in the bog of the unsettled Barbaric Archipelago. After which, he declared that as long as his boot remained in the bog, there would be Vikings in the Archipelago.
Great Hairybottom left a huge impact on the course of history of the Barbaric Archipelago. The legend of him losing his boot in the bog of the Archipelago was used as moral support for all the Vikings centuries later, during the time of Hiccup Horrendous Haddock III, when the Archipelago was at risk of being destroyed by the Exterminator dragons.