Answer:
The dragon is the ultimate symbol of evil in the poem. It lives alone and hoards treasure for itself, sharing with no one and having no use for the loot. Beowulf is the dragon's opposite, generous and willing to lay down his life to save his people from being destroyed by the monster.
Step-by-step explanation:
Good and evil in Beowulf relate to the idea of selflessness versus selfishness. Notice how the good characters tend to be generous, community-minded people, like the warrior kings who share treasure with their warriors or Beowulf who helps defend the innocent from the claws of Grendel. Notice how Grendel and his mother, both presented as violent and malignant, are anti-social outside of their interactions with one another. They are threats to the community, which in the poem is presented as the highest good.