Jethro Tull
There are certain riffs that are forever emblazoned in the soundtrack of rock and roll: the Beatles’ “Day Tripper,” the Stones’ “Satisfaction,” the Kinks’ “You Really Got Me,” Cream’s “Sunshine of Your Love,” Hendrix’s “Purple Haze.” Then there’s the opening guitar lick to “Locomotive Breath,” the inevitable showstopper at any…