The Olafs are a group of vikings only seen in the episode Dear Vikings. It is unknown why all their names are Olaf. But it could be they all named themselves just for the fun of it, or because Olaf is (or was) a popular scandinavian vikings name, so they were all named that. They like playing "Shield Toss", as well as "Flaming Shield Toss".
The Olafs all have different color skin and beards and they wear viking's hats.