Before he arrives at Heorot, Beowulf is famous for having the strength of thirty men. When he arrives at Heorot, Unferth, annoyed by Beowulf's presence, questions Beowulf's heroism, announcing to all that Beowulf was defeated by Breca years ago in a swimming contest and that Beowulf will surely meet his match in Grendel. Beowulf corrects him, stating that he was stronger and faster than Breca and that he was even "reluctant to leave him" behind. On top of this, Beowulf says that during this contest he was able to kill nine sea monsters. Beowulf continues:

Now I cannot recall
any fight you entered, Unferth,
that bears comparison. I don't boast when I say
that neither you nor Breca were ever much
celebrated for swordsmanship
or for facing danger on the field of battle.

Any thought that Beowulf is inflating himself through his words is put to rest when Beowulf takes on and defeats the monster Grendel. Grendel has been terrorizing the mead hall by killing and eating Danish warriors. Grendel openly and mockingly enjoys the way he can disrupt and harm human life without any consequences.

Nobody has been able to defeat this monster, but Beowulf faces him bravely and tears off his taloned arm, killing him. By destroying Grendel, Beowulf greatly increases his fame. He becomes even more renowned when he takes on and kills Grendel's powerful and vengeful mother. Finally, Beowulf cements his fame late in life when he kills a dragon that has been imperiling his people. This costs him his life, but he dies honorably and victoriously.

Beowulf arguably exemplifies the importance of physical strength and courage in Anglo-Saxon culture. In the centuries after the fall of the Roman Empire, small pockets of civilization depended on the bravery of such warriors to protect them from outside threats.