Once, a mighty hero aided a golden dragon in her quest to save the world from hellbeasts, who were threatening to rise up and overtake the realm of the living.
In thanks for his noble efforts, the golden dragon crafted a beautiful and magical dragonscale shirt for the hero - so that he and his line may forever be protected from harm by the magic of the dragon kin.
Now here we are, three generations later - and Derek has inherited the shirt down the line. What a tosser. Derek is a real knobhead - surly, mean, and drunk. The kind of guy you get when you make him and his family completely untouchable by anybody.
Derek is a mercenary - he works for whoever will pay him the most. And, despite having almost no combat skills or intuition, he gets hired - because the magic of his dragonscale shirt makes him untouchable. And so it will continue, until he drinks himself into an early grave - and whatever poor bastard kid he spawns gets to inherit the dragonscale shirt and start it all over again.
(That is, of course, unless he can fall in love and find himself in a situation where he raises his kid well - or if he runs into the ancient golden dragon so she can realise what a mistake the gift was and revoke it - or if he meets up with the person who has a dragonfang sword - or otherwise get himself a lesson in humility)