You know, I do wonder where Wiglaf get's his reputation from. Is he known for going on berserk rages? I mean, it can't simply be that he's "the greatest Hero in the world", as stated in the last chapter. Hero's successfully foiling schemes and plots is the primary part of the job description, after all. Being someone who forgives personal grievances is also in the job description, under "Preferred, but unrequired, traits", suggesting that it's a trait that the "Greatest Hero in the World" should have.

That said, he needed to be called the "Devil of Bohuslän" for some reason. Though there is a possible slight implication that he was named to be in opposition to a certain Villain's Name (one that I have accidentally listed in the comments previously, without realising it wasn't directly mentioned. I broke my unimportant self-imposed rule!). Of there could be another reason, such as them having a troubled childhood and growing up in Bohuslän, though, before being given the name before they became famous.