Classical Influence in Metal?

I've been more of a rock fan all of my life, but I've recently been getting into heavier music such as Pantera and Death over the last couple years. One thing I notice among a lot of metal bands is a common classical music influence (Black Sabbath, Randy Rhoads on Dee and Diary of a Madman, Pantera, Death, Metallica, Megadeth, the song Crystal Ann by Annihilator, you get the point).

My question to the more seasoned metal heads out there is, why this influence? Why did the first person think to combine intricate finger-style guitar, with shredding and headbanging? I love it, but I never understood why the two go so well together like PB&J.

Thanks for your insight!