Iron Man is possibly Black Sabbath's most popular song from their second studio release "Paranoid" in 1971. This is one of my all time favorite Black Sabbath songs and is actually the first one that I learned. It starts with that recognizable droning open E string. You can actually hear Tony Iommi bending the open note by bending it behind the nut on the tuner, which gave it that distorted, drone-like and almost vocal sound in the beginning. Then he goes into that iconic sliding power chord riff, taking a chord shape and moving it around up and down in the pentatonic pattern. The verse mimics that power chord shape but plays it instead with single notes. Tony's playing is has great vocal characteristics and the tone was able to get out of the gear at the time was revolutionary.