What causes the awakening of the dragon in Hygelac?

Answer: The dragon is awakened by the sound of the footsteps of a runaway slave.

Explanation:

The dragon is Beowulf's main opponent, which ultimately brings him down. Beowulf succeeds in fighting Grendel and his mother, and proves to be a real hero.

Fifty years after Beowulf has defeated these two enemies, the dragon is awakened by a slave who steals a cup from its treasure. It then attacks people, seeking revenge. Beowulf fights with it, and receives a death - wound.