Beowulf is best described as an early epic hero. What are his heroic qualities and flaws and how does he manage to reconcile both with all he has to accomplish?
He has great physical strength: he defeated several sea monsters during a swimming (or possibly rowing, depending on the translation) contest against his childhood friend Breca, and defeated both Grendel with his bare hands and Grendel's mother by wielding a sword forged for a giant.
He is honorable: when King Hygelac dies, instead of starting to campaign and claim the throne for himself because he is a popular warrior, he supports Hygelac's son and heir.
He is willing to sacrifice himself to defend his people against a dragon that was terrorizing the countryside. He is braver than younger men, and stronger, too--he ultimately defeats the dragon, but dies from his battle wounds.
On the other hand, he has a huge ego and is constantly hungry for glory. While this is understandable given his successful warrior career, it also meant that he takes huge risks--and as a king, a risk to himself is also a risk to his people. By taking on great risks, Beowulf opens his throne up to potential instability, and does a disservice to his people by dying and leaving the throne open. While the narrator doesn't give a final judgment on Beowulf's behavior, he does point out that a king is responsible for the well being of his subjects, not just for his own glory.
Beowulf reconciles these by prizing bravery and success in battle over his own life, and glory over continuing to rule his people. He is a good, brave, and just ruler while he is on the throne, and while he may be accused of being egotistical and overhasty in taking on a fight beyond his abilities at the end, he also accomplishes his mission--taking down the dragon.