In the epic poem Beowulf, the reason Beowulf's memory is kept so alive is dependent not only on Beowulf's feats of heroism, but also on the efforts of scops (storytellers) that repeated the list of his accomplishments with poetry and accompanying music.
Beowulf is a larger-than-life-character. He comes to offer his services to the Danes for a battle that will bring him no tangible rewards: he selflessly puts his life on the line for others, hoping to be of service as he has heard of the suffering of the Danes—which has lasted twelve winters. Our hero is keenly in tune with his sense of honor and duty not most importantly for his own sake but for the way his behavior reflects on his feudal lord and uncle, Hygelac. He also is not interested in taking the easiest route to success: if the monster Grendel attacks the mead hall with his bare hands—unaided by weapons—Beowulf will meet him on the same terms.
All of these unselfish characteristics, as well as his obvious sense of honor and duty, make Beowulf a hero that outshines other men who might have tried to battle Grendel in the Hall of Hart, and lost. Beowulf does not measure himself by the same criteria of common men, and he becomes a legend.
If Beowulf's actions are not enough to provide him with a persona of mythical proportions, the storytellers of the time passed his tales of glory down through the oral tradition, saved and savored for hundreds of years to come before they were finally recorded in writing. The language the scops and bards used was eloquent and magnificent. Literarily, tales of Beowulf would have been told with masterful descriptions. The storytellers would have evoked the imagination of their audience, and would have made this epic poem beautiful to listen to based upon the grandeur of their speech. The language was limited, having no metaphorical base, so kennings— Anglo-Saxon metaphors—would have been used to add to the dramatic recounting of Beowulf's enormous accomplishments, not only as a warrior, but ultimately as King of the Geats.
The character of Beowulf remained memorable not only because of his great deeds and strong sense of honor, but also because of the way these deeds were "immortalized" through the efforts of countless storytellers and bards over many, many years.