Beowulf is an early epic, whose “themes” are heroic actions against an antagonist. The function of epics is primarily to record the deeds of the hero in the historical context that brought the conflict into focus. This epic differs from several others
(for example The Iliad) in that the protagonist has non-human characteristics, and as such, the “theme” is affected in this regard: some conflicts for the hero are not against human antagonists but natural or subhuman antagonists. Grendel, despite his detailed description, is an abstract enemy, a negative force preventing the inhabitants of Heorot from completely enjoying their victory. To modern readers, the “theme” then is that heroism can be expressed even against abstract enemies, even self-inflicted “beasts” – addiction, cultural injustice, etc. This is one reason why Beowulf has maintained its popularity even into modern times, and has generated spin-offs such as John Gardner’s Grendel and the movie (which concentrated on the action rather than on character development).