The Black Sabbath compilation "We Sold our Soul for Rock'n'Roll."
When I was in grade school and early middle school all I really listened to was the oldies radio station that my parents listened to. "Paranoid" was in the rotation but that isn't what made Sabbath click for me.
I loved football and played football. The college football team from my state had a pretty awesome marching band. I remember watching a game and the band had worked in the Iron Man riff into their repertoire. I didn't know what it was, but I loved it - just the main riff is all they played over and over. I was at football practice the next day and I asked my friends if they heard it and what it was? Black Sabbath - Iron Man said my buddy. That was all she wrote.
Thinking back on it, the Iron Man riff conveyed more than just "coolness." It was more like an event, something was at stake, you were meeting your fate, etc.
I remember my buddies' older brothers listening to Deicide, Morbid Angel, Slayer, and Seputura - but that stuff scared the shit out of me back then!
Sabbath I could handle!
A few years later I somehow ended up with Amorphis - Tale from a Thousand Lakes and Sepultura - Beneath the Remains. Those are the earliest albums that I can recall that are reviewed on DLA.
But I find it interesting and appropriate that what hooked me on metal was metal being played by a marching band and it had nothing to do with the "aesthetics" of metal.