Grim Gruesome Viking villain in The cursed sword

The story is set in a larger-than-life Viking world, where Bjarni the pigboy and Astrid, the landowner's daughter have a budding romance and no future until a massive and mysterious figure looms out of the mist. He says he is Astrid's uncle and suggests that Bjarni should try making his fortune as a pirate. But it isn't giving too much away to reveal that this is Grim Gruesome himself and he soon has both children firmly under his spell. He is an unredeemable monster, who just hates children, for no apparent reason, but hasn't allowed for how resisitant these two are.