Designer Virgil Abloh became the first Black American to hold a top creative job at a major luxury label. Abloh, who was artistic director of menswear at Louis Vuitton, was able to turn ordinary streetwear like hoodies and sneakers into high fashion, commanding big price tags and drawing celebrity customers. WSJ's Jacob Gallagher unpacks the legacy of Virgil Abloh, who died earlier this week at age 41.