Beowulf was born to be extraordinary. His early heroic deed involved setting off into the sea with a friend and being the only one coming back alive. He “proved more might in the sea than any other man, and more endurance in the ocean” (ch 8, p. 14) when he outswam his friend and fought off the sea-fish. An epic hero usually does have an early deed that shows his ability to accomplish an amazing feat.
Of course, it was Beowulf’s defeat of Grendel that cemented him as the epic hero.
His sinews ripped apart and his bone-frame broke. victory was now given to Beowulf, and Grendel, sick unto his death, went hence and sought his den in the dark moors, that vile abode; he knew full well that his life had reached its end and that the last of his days on earth had come. (Ch 12, p. 18)
Beowulf is able to kill Grendel with his bare hands and brute strength, and his exploits are sung in praise throughout the kingdoms.
An epic hero is one who has legendary characteristics and heroic, unselfish actions. He takes no thought for his own safety but focuses on the good of others.
Beowulf takes on the Grendel and Grendel's mother, achieving what others had not been able to do. He was able to save the people from their oppression, which taking on great danger to himself.
In the end he takes on the great dragon, at mortal danger to himself, to protect the people.