The motif of heroes and monsters is quite a prominent one in Beowulf. Let's first start with the motif of a hero.
If you think in terms of this epic poem, the most obvious example of a hero is Beowulf himself. He is a strong and chivalrous man, not afraid of anything, always ready to fight and defend those in need. He has many heroic characteristics, which made him a king thanks to his adventures.
On the other hand, there are more examples of monsters in this poem. The most obvious one would be Grendel. He is a creature of the night, a murderous beast who kills people only because he is jealous of them. He is evil, and due to his actions he has to die. Apart from him, examples of monsters would be Grendel's mother, as well as the dragon in the end.
