Funnily enough, Doom was what got me into Metal.
It's a very intricate story. First I heard about John Romero's SIGIL thing, and how this guy named Buckethead did a soundtrack for it. I checked out the "Romero One Mind Any Weapon" track, thought it was awesome, and went down the rabbit hole, finding bands like Megadeth, Cannibal Corpse, Iron Maiden, Pantera, among others.