Originated from the immortal one. Upon his defeat of the dragon that was protecting the treasure of Nibelung, the blood of the dragon poured over his body and solidified his skin like armor. Thus, he became an immortal warrior. From that time on, he has received so many nicknames, such as dragon slayer, the one who slew the dragon, etc. It is said that he was finally killed when a spear penetrated his body through a spot that the dragon blood hadn't reached. I guess no one's perfect.