Sam Phillips, founder of Sun Records in Memphis, Tenn., was in his studio on Dec. 4, 1956, the day four of music’s biggest names dropped by. Elvis Presley, Johnny Cash, Jerry Lee Lewis and Carl Perkins, each a distinctive artist in his own right, were enjoying an impromptu jam session when Phillips had an epiphany: He was listening to a “Million Dollar Quartet.” Dashing outside, he buttonholed a reporter to make certain the event was photographed.