Passage: Later in his life, Beowulf becomes king of the Geats, and finds his realm terrorized by a dragon, some of whose treasure had been stolen from his hoard in a burial mound. He attacks the dragon with the help of his thegns or servants, but they do not succeed. Beowulf decides to follow the dragon to its lair at Earnanæs, but only his young Swedish relative Wiglaf, whose name means "remnant of valour", dares to join him. Beowulf finally slays the dragon, but is mortally wounded in the struggle. He is cremated and a burial mound by the sea is erected in his honour.

Question: Beowulf found that it's realm was being terrorized by what?
dragon