In most respects, Beowulf is a good king. As a young warrior, Beowulf abides by the Anglo-Saxon values of the comitatus. This set of values emphasizes the interconnection of loyalty, bravery, and generosity. Most notably, the young warrior fights with bravery and loyalty for the king, who rewards the warrior with generous gifts. Each does what he can to protect the society from enemies and to bring glory and fame to the kingdom.
Beowulf and Hrothgar display this relationship in Beowulf's coming to the Dane's defense against first Grendel and then Grendel's mother. Apparently, only Beowulf was capable of fighting these monsters. Interestingly, in the prologue to the poem, Hrothgar's ancestor is praised for qualities we find Grendel possessing as well. In Seamus Heaney's translation, we read
There was Shield Sheafson, scourge of many tribes,
a wrecker of mead-benches, rampaging among foes.
This terror of the hall-troops had come far.
A foundling to start with, he would flourish later on
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