In 1996 he was a biomedical engineering student at Vanderbilt University. Today he's a heavily bearded outlaw country superstar with a diamond-certified record who sang the national anthem at the Super Bowl. Chris Stapleton's path from science lab to the top of the Billboard charts is one of the most improbable stories in country music.

Before the spotlight, Stapleton spent 15 years as Nashville's invisible engine, ghostwriting roughly 1,000 songs for other artists and running what amounted to clinical trials on his own sound. By the time he signed with Mercury Nashville in 2013, he had quietly engineered a voice no one in country music could ignore — proof that patience and ruthless curation beat overnight success.

• Stapleton wrote 1,000 songs for other artists across 15 years before taking center stage

• He left ...