In the 1950s, nude photos of male celebrities were practically non-existent; the few examples we have were taken and developed in private, and didn't get mass exposure for many years. Even shirtless photos are uncommon. So it's no wonder that Elvis Presley caused a stampede when he was photographed in his underwear during his induction into the U.S. army in 1958.
At the time he was the most famous singer in the world, a cultural icon who almost single-handedly drew rock and roll away from its roots in jazz and blues. He had already had a string of #1 hits, including "Heartbreak Hotel," "Blue Suede Shoes," "Don't Be Cruel," "Hound Dog" -- the list goes on. Being drafted was a big deal, even without the underwear.
He was apparently quite homophobic in real life -- most men of the 1950s generation were -- but that didn't stop him from forging friendships with many gay men.