A 10-year-old boy storming off to his bedroom after a fight with his brother accidentally invented the three-finger roll that changed the banjo forever. Earl Scruggs took an instrument known as a comedian's prop and turned it into the driving engine of bluegrass music, playing rhythm and lead at the same time with a sound like thumbtacks plinking on a tin roof.

From a North Carolina textile mill to a 1945 Nashville audition that floored Lester Flatt, Scruggs's story is one of relentless innovation: he drilled into his own prized banjo to invent new hardware, and he risked his conservative fan base to keep his music evolving, even sharing an anti-war stage with Steppenwolf and the Byrds in 1969.

• He discovered the revolutionary three-finger roll by accident while blowing off steam at age 10

• At 21 he auditioned fo ...