Rap shook up the music business this year, dominating popular culture like never before, and experts say Metro Boomin is a big reason why.

The St. Louis-born, Atlanta-based producer’s distinctive mix of heavy bass, rattling synthetic percussion and dark, gothic melodies has ruled the singles charts in 2017. On the Billboard Hot 100 dated Nov. 25, Metro Boomin produced 10 songs—10% of the chart—with four tracks in the Top 40. His sound has even permeated the highest echelons of pop music. Taylor Swift’s new album, “Reputation,”...