^Barnet & Burriss 2001, p. 87 "It was not so much the music as it was his over-the-top theatrical stage show that made him instantly infamous. Thus, Alice Cooper started what many pop music historians believe was the first true prototype for heavy metal."
^ abcWalser 1993, p. 10 "The sound that would become known as heavy metal was definitely codified in 1970 with the release of Led Zeppelin II, Black Sabbath's Paranoid, and Deep Purple In Rock."
^Hoffmann & Ferstler 2005, p. 454 "A populist blend of heavy metal and updated blues boogie, Grand Funk Railroad provided a model for rock band successes in the 1970s."
^Frith & Goodwin 1990, p. 85 "The lack of intermediary strata between heavy metal audiences and groups was further determined by another characteristic of the music. Most of the groups that were predominant - Led Zeppelin, Black Sabbath, Uriah Heep, Humble Pie, Deep Purple, and so on - were British."
^ abWalser 1993, p. 10 "A "second generation of heavy metal," the first to claim the name unambiguously, was also active throughout the 1970s: KISS, AC/DC, Aerosmith, Judas Priest, Ted Nugent, Rush, Motorhead, Rainbow, Blue Öyster Cult. Scorpions, from Germany, became the first heavy metal band from a non-English speaking country to achieve international success."
^Everett 2008, p. 267 "Iron Butterfly's "In-A-Gadda-Da-Vida" may prove more influential to the post-'60s future of heavy metal than the more often-cited Led Zeppelin in the nonfunctional and nondiatonic basis of its chord relationships."
