But the Elvis Presley remembered by Joe Moscheo, a gospel singer who sang backup vocals for Presley as a member of the Imperials, was a deeply spiritual man who would leave screaming fans, retreat to his hotel suite and croon old hymns until dawn.

"When he left the building," Moscheo writes in his forthcoming book, The Gospel Side of Elvis, "most nights, Elvis wanted nothing more than to go somewhere with a few friends and a piano, a place they could gather to sing and listen to the gospel music that nourished the heart and soul of this American musical and cultural icon."

Thirty years after his death, Presley is better known more for his spot in the Rock and Roll Hall of Fame than his place in the Gospel Music Association (GMA) Hall of Fame.

But his gospel side is a rich one. Some of his first recordings were songs like "Softly and Tenderly (Jesus is Calling)." He won two Grammys for his gospel albums, "How Great Thou Art" and "He Touched Me," and according to John Styll, president of GMA, there is the simple "fact that he loved gospel music."

"Some of the people he admired most were African-American gospel singers," said Moscheo, 69. "He admired them, embraced them, and bragged about them. He was a student of their music. He learned a lot from them and gave them credit."

Michael Bertrand, a history professor at Tennessee State University and author of Race, Rock and Elvis, believes Presley's music -- especially the way he effortlessly integrated black musicians like the Sweet Inspirations into his acts -- prompted a younger generation to question their conventional prejudices.

"Suddenly you have kids questioning: ‘I really like this (music). Why should I not like this? What's the big deal, why shouldn't I have African-American background singers?'" Bertrand said.

Church attendance was problematic
Presley was raised in a soul-filled Assembly of God church in East Tupelo, Miss., but faced difficulty attending church as his popularity soared. After he nearly started a frenzy one Easter Sunday at the First Assembly of God Church in Memphis, he decided to limit his spiritual diet to gospel music recordings and Sunday sermons from his favorite TV preacher, Rex Humbard.

That's why, Moscheo speculates, Presley's after-hours gospel singing and his well-worn gospel records gained greater significance for Presley as a sort of personal time with God.

As his career progressed, though, he began experimenting with numerology and astrology, but Moscheo maintains that Presley never departed from his Christian roots.

"He didn't ever give up notion that he was a Christian. ... He knew his roots and what his mother had taught him."

For Moscheo, his friend will always be "the greatest gospel singer that ever lived," because the words, the inflection, the timing of his songs showed he connected with a higher power.

"When you're praising God through a song, it comes through at the right time, with the right phrasing," Moscheo said. "When it's time for a word to be important, it comes out."