Mooney died Sunday at his home in Kennedale, Texas, of complications from cancer, said his wife, Wanda.
Although he had slowed down in recent years, he still played and recorded periodically until near the end of his life. He played on four tracks on Marty Stuart's 2010 Grammy-winning album "Ghost Train: The Studio B Sessions."
"He was my all-time country music hero as far as musicians go," Stuart, a longtime friend, said Monday. "When I was making the 'Ghost Train' record, I took it to California with me. I was listening to it as I was driving down Victory Boulevard, and when I heard him play I started crying, because it was always my dream of going to California and hearing my music sound like that."
Mooney took the instrument to the forefront of the twangy and punchy California brand of country with his clean, high-profile accompaniment and soloing when he was a member of Stewart's band in the 1950s.
"Ralph Mooney was one of the chief architects of the 'Bakersfield sound,' " said Chris Hillman, a founding member of the Byrds and the Flying Burrito Brothers. "Nobody played steel like Ralph....When Ralph took a solo, you knew it was all California."
Mooney's work as a top country session player for Capitol Records in Hollywood in the 1950s and '60s helped revitalize the steel guitar's role in country music at a time when Nashville producers were veering away from the instrument to create a more broad-based, orchestra-laden style that became known as the Nashville sound.
As a songwriter, Mooney co-wrote the country classic "Crazy Arms," which became a No. 1 hit for Ray Price in 1956, and has been recorded by Jerry Lee Lewis, Willie Nelson and numerous others. "I would starve to death if it wasn't for those royalty checks," Mooney once said.
When Jennings hired him to be part of his Waylors band in 1970, it was because "Waylon always said, 'Hell, there's only one steel guitar player, and it's Ralph Mooney,' " Jennings' longtime friend and drummer, Richie Albright, said in the liner notes for the 2006 box set "Waylon — Nashville Rebel."
"He was a pioneer and a visionary," Jennings' son, country-rock musician Shooter Jennings, said Monday. "He coveted his instrument and ultimately improved it. I feel he was one of the last keys to the old 'outlaw' sound and now it's gone forever. Thanks God for those albums."
Mooney played on the song "Ladies Love Outlaws," Jennings' first to use the word that became so integral to the freewheeling music he and Nelson would make in the '70s and '80s.
But he was already a star on his instrument when Jennings drafted him.
He had been named steel guitarist of the year by the Academy of Country Music in 1966 and received six more nominations for that honor over the next 15 years. He was inducted into the Steel Guitar Hall of Fame in St. Louis in 1983, and his induction plaque reads, in part, "So uniquely original that he remains unduplicated."
Mooney was part of the studio band that played on most of Buck Owens' earliest hits. He came up with the sharp, snappy opening notes of "Under Your Spell Again," "Above and Beyond," "Excuse Me (I Think I've Got a Heartache)" "Foolin' Around" and other hits that helped put Owens repeatedly into the Top 10 of the country singles chart in the late '50s and early '60s
Once Owens had formed his band, the Buckaroos, which would back him live and in the studio for most of his career, Mooney contributed key melodic ideas and support on hits for Merle Haggard, including "Swinging Doors," "Sing Me Back Home" and "The Bottle Let Me Down," as well as other California-based country stars such as Stewart, Rose Maddox and Bonnie Owens. He wasn't limited to West Coast country community, and also played behind Wanda Jackson, Donna Fargo and Jessi Colter, Jennings' wife.
"He played with a real bright, animated sound with lots of picking, but he could take off into blues licks at the same time," Michael McCall, writer-editor at the Country Music Hall of Fame and Museum in Nashville said Monday. "Nobody every played quite like he did, and after that it became known as 'the Mooney sound.' When anyone brought up what he did with Buck and Merle, Ralph would say 'I always call myself Wynn Stewart's steel player, because he was first.'"
Mooney was born Sept. 16, 1928, in Duncan, Okla., and moved west as a boy to live with one of his sisters in California. He learned to play guitar, mandolin, fiddle and a flat-top guitar using a knife for a slide. Later, he built his own steel guitar with a design that influenced the instruments that came out of electric-guitar innovator Leo Fender's factory in Fullerton.
After working for Douglas Aircraft, Mooney joined Skeets McDonald's band, then connected with Stewart, a pioneer of the Bakersfield style of country, which was louder — thanks to its use of then-new Fender solid-body electric guitars — and more rhythmically propulsive than what Nashville studios were turning out in the '50s.
Besides his wife of 62 years, Mooney is survived by son Richard, daughter Linda Yates, four grandchildren and two great-grandchildren.