The book The Jordanaires: The Story of the World's Greatest Backup Vocal Group (as told by Gordon Stoker) is currently available online at Loot.
The synopsis includes the following:
The greatest backup group in the history of recorded music undoubtedly was The Jordanaires, a gospel group of mostly Tennessee boys, formed in the 1940s, that set the standard for studio vocal groups in the 50s, 60s, 70s, and beyond. In their 65-year career, from 1948 through 2013, the recordings they sang on have sold an estimated 8 billion copies.
They sang on about 260 Elvis recordings, including most of his biggest hits. They were in 3 of his best-known movies, appeared with him on most of his early nation-wide TV shows, and toured with him. Throughout Elvis' early career, they were his most trusted friends.
How did The Jordanaires come to sang backup for Elvis?
Well, one hot August night in 1955 The Jordanaires were in the Ellis Auditorium in Memphis appearing on a bill with Eddy Arnold. That night they were approached backstage by Elvis Presley, then a struggling singer who had had some success and was hoping to make it big.
In his book, Gordon remembers:
I guess the first thing I remember about him was his shirt. Men just didn't wear pink shirts in those days. He also was a little dirty around the neck. He was polite and had a warm smile. So, when he approached me, I took the time to hear what he had to say.
What he said was, "I'm a big fan of y'all's. I'm a singer myself. I'm on the Sun label right now. That's a local Memphis label. I'm trying to get a deal with a major label. If I do, I'd like you guys, the Jordanaires, to sing with me on my records.
The rest is history.