In Richard Wagner's opera cycle, the dwarf Alberich turns himself into dragon to convince the gods of his power after he has claimed the Gold of the Rhienmaidens for himself and turned it into a magic ring. Later on in the story the giant Fafnir also turns himself into a dragon (obviously a popular pastime in Norse mythology) to guard the gold which has now come to him. The dragon gets killed by the upstart hero who is later stabbed in the back. Nobody has a happy ending; it is opera after all.