You hear a voice in your head
"Once upon a time there was a foolish young dragon named Mjolnir.His grandam had told him to leave humans well alone,but he would not listen to her.
He was of the age when he was trying out what was good to eat and what was not.Eventually he decided to try a human.It was a young female and its soft meat tasted juicy and good in young Mjolnirs maw.
Things went from one to another and soon Mjolnir found himself outside the city gates of the humans demanding more of this delicacy.The terrified humans began feeding Mjolnir several of their female young.
His grandam protested,but the cocky young dragon ignored her.He'd been kind of surprised when the humans had caved in so easily to his bellows.But who was he to look a gift horse in the mouth.
This went on for several years till a holy human by the name of George came riding in an ran a lance through Mjolnirs body.George and Mjolnirs next meal rode off and the young dragon was left dying in the cave.
He heard a voice"Mjolnir my beloved son,what hast thou done"It was the voice of his grandam,who had died a year earlier and gone to that great lair underground where all dragons go when they die.
She told him he was unworthy to join his ancestors,and only when he
had got a human to perform 12 labours would he be free to join his ancestors.Then there was a flash of magical energy and where Mjolnir once lay dying lay a golden medallion with a engraving of a imprisoned dragon on it.
"I am that medallion,so spaketh Mjolnir"booms the voice in your head.