"Smoke on the Water" is known for and recognizable by its central theme, developed by guitarist Ritchie Blackmore. It is a four-note blues scale melody in G minor, harmonized in parallel fourths. The riff, played on a Fender Stratocaster electric guitar by Blackmore, is later joined by hi-hat and distorted organ, then the rest of the drums, then electric bass parts before the start of Ian Gillan's vocal.