After reading up on the legend, it looks like his trusty side-kick Wiglaf, actually helped him to defeat the dragon but Beowulf still loses his life. It's funny because in that scene where Wiglaf is riding the horse up the steps and Beowulf sees that his short sword is not long enough to reach the dragon's heart, I thought for sure he was going to toss him either a long sword or a spear to help him finish off the dragon. But nooooooo! They had to go with this over the top rubbish where he cuts off his own arm to give him the extra reach he needs. I hate when they do dumb shit like that. The story would have been perfectly fine with Wiglaf helping him slay the dragon (like the legend goes) and Beowulf simply dying from the fall as the dragon collapses. Hollywood always gotta fuck shit up.