Meet Fafnir, our Norse Dragon

Originally a compelling shape-shifting dwarf, (or a powerful dwarf magician, depending on source material), Fafnir became corrupted by greed for his father's gold. He killed his father, and according to some accounts also his brother (or brothers) in order to claim all the gold. He fell asleep on top of his coveted gold, and as he slept changed into a nasty tempered, gold-hoarding, mean spirited, cave dragon.
Fafnir breathes a venomous mist, NOT fire, as do most other dragons. This mist surrounds his lair, and humans and heroes breathing it lose all courage and usually die before being able to battle Fafnir, let alone kill him.
Do NOT confuse this dragon (Fafnir) with Barney the purple dragon from Sesame Street, (who is actually a purple dinosaur anyway),
nor with the familiar gold-hoarding dragon, Smaug, from Lord of the Rings/The Hobbit.
Fafnir is unique, as are all dragons.