Update 2/24/2015: If you are reading this, how did you get here? Why does this post have 2500 pageview? Who are you people? Reply in the comments please.
I strugled long and hard to come up with a superhero comparable to Beowulf, largely because Beowulf does not meet many of the requirements for a traditional epic hero. He does not have a weakness, other than his habit of breaking any weapon he uses.He is never defeated, save for at the end of his life when he decides that it is time to die. He frequently boasts of his assorted escapades, always over a hefty mug of mead. In short, he is a pretentious overpowered braggart of a superhero. Then it hit me. Thor (the Marvel superhero, not the Norse deity, although many of the same points probably still apply) is an excellent match to Beowulf. Thor's superpowers include massive strength, skill at combat, and invincibility to normal weapons; these "standard superhero" powers are vastly exceeded by his ability to fly, time travel, and throw Mjolnir the magic hammer. Thor is so massively overpowered that his creators have to challenge him by throwing absurdly powerful enemies into the fray, which he often defeats with little to no effort. In the recent movie adaptation of Thor's comic book series, a band of noble warriors is about to be messily killed by a towering ice-monster, only to be rescued by Thor, who kills the beast by flying in through its gaping maw, through its skull, and out the back of its head. The entities who pose any significant threat to Thor can be counted on one hand; they include his similarly-powered brother, Loki, and his normally-benign father Odin, who is often forced to punish Thor for being insolent and disobedient. His only significant weaknesses lie in direct damage to his hammer, since his soul is bound to it, and in various arcane cosmic forces far more powerful than himself. Similarly, virtually nothing can defeat Beowulf. After significant buildup, he defeats the mightily enchanted monster Grendel by ripping its arm out of its socket, intentionally forgoing the use of any sort of weapon in favor of his vast strength. This is the same Grendel that forced a mighty tribe of warriors to abandon their grand hall, lest they be devoured in the dead of night. The lesson of this encounter is that Beowulf is simply so powerful that he can defy the limits of what is usually considered feasable. When he is ultimately defeated by the great dragon at the end of the story, Beowulf senses that his time has come, and goes to his death entirely by choice. Even in defeat, he manages to slay the dragon, even while dying from massive wounds. There are a number of notable differences between Thor and Beowulf. Notably, Beowulf, a mortal yet powerful human, dies at the end of his story, while Thor, and immortal deity, keeps going through many events that should by all rights kill him. At the end of the movie Thor, the title character experiences a change of heart and conscience, coming to recognize the value of self-sacrifice and mortality, emerging an improved individual. Beowulf, on the other hand, was already a perfect hero from the start, and remains a static character throughout. Interestingly, Thor is closer to a traditional hero than Beowulf. Thor has a number of well-defined weaknesses and extracts a measure of self-development from his quests, while Beowulf is virtually invincible and remains unchanged through the story. Beowulf idealizes the values of his culture in that he exaggerates them beyond all reason, into the realm of pure myth.