Robby Turner, the pedal steel guitarist whose soulful mastery of the instrument is embedded in stardom-redefining songs for Waylon Jennings, Sturgill Simpson and Chris Stapleton, has died. He was 63.

The guitar, the banjo, the mandolin, the fiddle, and the upright bass are just a few of the instruments commonly associated with country music. Though there is one instrument missing from that list, ...