The epic poem Beowulf has an interesting trait, and it is that it mixes elements of paganism and Christianity. when it comes to the Christian elements, we find that Grendel, the dragon, and his mother are described as descendants of Cain. In Christianity, Cain and Abel are recognized as the sons of Adam and Eve. Presumably, Abel was the good son, while Cain was the bad one. According to the biblical story, Cain killed Abel and is known in the faith as the "kin killer".
It is also accepted in Christianity that all the descendants of Cain would be monsters, and other destructive beasts that represent the sins of the human race. Therefore, the fact that Grendel and his mother are described as descendants of Cain implies that they represent the forces of evil. Contrarily, Beowulf and his people are representative of the forces of all that is good, because both God and "the fates" gave him a mission to fulfil. The fact that he fulfilled this destiny and defeated Grendel and his mother (evil) is what gave him his quality of superhero.