Beowulf vs. Beowulf. This essay goes into detail about who Beowulfs real enemy is.

As one nears the end of Beowulf, it becomes clear that Beowulf's real enemy is not some monster lurking in the murky waters of the sea, nor a vengeful mother wanting to defend her murderous son's death, and especially not some fire breathing dragon waiting in the dark shadows of a cave. Many persons or things seem to be causes of Beowulf's death. However, if we were to closely examine the entirety of the legend, …

…There is always something that is bigger and better (What's bigger and better than a dragon anyway). But the dragon is not the enemy...had Beowulf not strived to be the finest warrior of his time, he would not have placed himself in such a situation. If one's worst enemy is the only thing that eliminates one; then loyalty was the start of his descent, and the end; and now it has become his undoing.