One of the first documented times that the term "Heavy Metal" was used to describe the sound of a band was in 1971 when 19 year old rock critic (and later of punk legends Vom and the Angry Samoans) Mike Saunders used it do describe Sir Lord Baltimore's debut album Kingdom Come.
The big, ridiculous and over the top mutation of blues rock they did didn't catch on back then but nowadays it's not uncommon to hear them cited as an influence on many a rock-n-roll band with a penchant for something a little grungy, sludgy or stoned sounding.
What are you listening to tonight?