Morgan Wallen’s band members have a name for his hairdo: the Tennessee Waterslide. You have to have a certain boot-and-blue-jeans swagger, good humor, and lack of self-importance to pull off a mullet in the 21st century, but Wallen has all that in spades, not to mention a taste for sounds that belie the look. Of course, with a voice steeped in Appalachian smoke, country is practically Wallen’s birthright. He was born in 1993 in tiny Sneedville, Tennessee, and grew up singing harmonies with his sisters in the church where their father preached. By 2014, he’d managed to get onto and eliminated from The Voice, but not before showing an innate versatility and relaxed style. His breakthrough came with 2017’s “Up Down,” a Southern-rock spring break anthem that radiated frosty-can cool with help from Florida Georgia Line. But his 2018 debut, If I Know Me, proved Wallen could ride solo on cleverly penned everyman hits like “Whiskey Glasses,” a honky-tonk heartbreak sing-along about getting over your blues with something a little stronger than beer goggles. As easy as his country goes down, Wallen stays committed to exploring interesting new directions. In 2019, he converted “Cover Me Up,” the signature song of anti-bro Jason Isbell, into a hymn of support for returning veterans. And in 2020, he not only held down “Heartless,” Diplo’s EDM foray into the Wild West, but dropped “7 Summers,” a soft-focus Eagles-style ballad about a boy who lost a girl because he wouldn’t leave his East Tennessee home. His third album, the sprawling, 36-track One Thing at a Time, arrived in 2023.