Beowulf is most well remembered for his great deeds in vanquishing Grendel, Grendel's mother, and the dragon, but before he even meets any of those he boasts of his singlehandedly fighting off several nikors when his ship sank far from shore. I don't think he ever gives much of a description of what nikors look like, but in a footnote of the version I read, the translator suggests that they may have been walruses. In any case they were fell sea-beasts, and the idea of an obscure, rarely depicted monster from a well known legend appealed to me.