Who created heavy metal? Tony Iommy. But, Tony might deliver pizza if Django Reinhardt didn't inspire him to keep playing. Django in jazz, Tony in rock, kind of two different industries. So, it's a case of Jacobs externality.
1) Brian May, PhD: "Tony Iommi is the true father of heavy metal"; Eddie Van Halen: "Without Tony, heavy metal wouldn't exist".
2) On the last day at the factory (Tony decided to quit 'normal' job to fully play music), a machine accidentally cut the tip of his middle and ring fingers. Future seemed to fall into pieces...
3) A mindful friend gave Tony a Django Reinhardt record. Django only played with two fingers, index and middle ones, for soloing..the other fingers were paralyzed due to a fire accident.
4) If the fire accident stopped Django, Tony's spirit might never rise again...and the world would never hear Black Sabbath, the template of heavy metal !!!
In sum, the essence/history of metal can be summed into three words: Never Give Up!..or rather in two words?: Jacobs Externality? Tony Iommi? Iommy-Reinhardt?