THAT SLIPPERY TERM aglæca ‘awesome opponent, ferocious fighter’ is a well-known cornerstone of Beowulf scholarship. Found twenty times within this poem – more than all attestations in every other text combined – the meaning of this term is contentious given that it is used not only of Grendel, his mother, and the other monsters of the poem, but also of Sigmund (the dragon-slaying member of the Vǫlsung family), and the hero of the poem himself, Beowulf. Yet although the implications of this are frequently debated, the usage of aglæca for both hero and monsters is just one example of the ‘intriguing number of intimate links between Beowulf and his most famous foe’, Grendel. Both are also termed healðegnas ‘hall-thanes’ (lines 142 and 719) and described as earm ‘wretched’ (lines 1351 and 2368); Beowulf is as strong as thirty men (lines 379–81), while Grendel has the strength to carry off thirty men during his first foray into Heorot (lines 122–3); and both are overcome with an overwhelming fury when in battle (lines 709 and 703). Many of the attributes common to Beowulf and this creature are also displayed when the hero comes to blows with Grendel's mother, the warrior mirroring both the earlier behaviour of her slaughtered son, and of the furious mourning mother herself.

During the scenes within which the hero grapples with the monsters, ‘the difference between non-human and human is perceived, in one sense, in terms of predator and prey/predation and agonistic contesting’, whereby Grendel and his mother ‘ravage like […] predator[s], whereas Beowulf insists on contesting with [them] like a conspecific adversary (that is, as a member of the same biological species)’. Grendel, in particular, stalks the hall at Heorot and devours the unfortunate Danes bones, blood, and all, but Beowulf ‘reject[s] the role of prey and […] establish[es] himself as Grendel's worthy opponent’. The animal role assumed by the monsters is not merely that of an unspecified predator which depredates upon those species weaker than itself, however, as both Beowulf and the Grendelkin are specifically associated with one animal in particular: the wolf.