It started as a joke. In July of 2014, Dwayne “The Rock” Johnson, the actor, former pro wrestler and hulk with a heart of gold, posted a self-mocking throwback photo on Instagram. There he was in all of his dated ’90s attire: a Steve Jobsian-black turtleneck, washed jeans and—slung around his waist—a brown leather fanny pack. A fanny pack on the Rock?! How absurd! Instantly, “Fanny Pack Rock” became a meme pinging about the internet.

The viral sensation reached a new peak when the Rock hosted “Saturday Night Live” last May:...