A rollicking vocalist and gifted harmonica player, Syl Johnson's blues-informed soul found respectable success as he toiled through the '60s and '70s, but took on a second life as later generations discovered his punchy, celebratory recordings. Johnson scored hits like 1967's "Different Strokes" and 1969's socio-political reflection "Is It Because I'm Black?" but he'd left music behind by the mid-'80s to focus on real estate and his chain of restaurants. As the years passed, samples from Johnson's songs found their way into multiple high-profile rap and hip-hop tracks, and new...