Fifty-six years ago today, on May 17, 1967, Glen Campbell had a career-changing day, although he likely wasn't aware of it at the time. It was on that date that the singer recorded "Gentle on My Mind," which was the title track of his August 1967 album.

"Gentle on My Mind" was written by John Hartford. So the rumor goes, the tunesmith penned the track after watching the movie Doctor Zhivago.

“Everyone’s made a whole lot out of that," Hartford said of his inspiration for the tune. "I know it gave me a feeling that caused me to start writing, but as far as saying it came from that, I don’t know. It just came from experience. While I was writing it, if I had any idea that was going to be a hit, it probably would have come out differently, and it wouldn't have been a hit. That just came real fast, a blaze, a blur.”

Glen Campbell Gentle on My Mind single

Campbell knew that he wanted to record "Gentle on My Mind" from the very first time he heard it. Hoping to convince his producer, Al De Lory, and record label, Capitol Records, Campbell gathered session players on his own, including then-rising star Leon Russell, to record a demo version of the song. The record label was so taken with the recording that the demo version was released as a single, and it became one of the biggest hits of Campbell's iconic career.

"Gentle on My Mind" earned Campbell two Grammy Awards in 1968, for Best Country & Western Solo Vocal Performance, Male and Best Country & Western Recording; Hartford also won two Grammys, for Best Folk Performance and Best Country & Western Song (Songwriter). The song was used as the theme song for Campbell's TV variety show, The Glen Campbell Goodtime Hour, and was released on several of his compilation albums, including Glen Campbell's Greatest Hits in 1971, The Very Best of Glen Campbell in 1987 and The Glen Campbell Collection (1962–1989) Gentle on My Mind in 1997.

The Band Perry also recorded "Gentle on My Mind," for the soundtrack to the documentary Glen Campbell: I'll Be Me. Their cover earned the sibling trio a Grammy Awards nod.

7 Songs You Didn't Know Glen Campbell Played On

Glen Campbell's name is legendary in country music thanks to his iconic hit songs, but he's also a major figure in music as a whole due to his crossover hits and, especially, because of his work as a session musician. Whether fans know it or not, Campbell left his mark on myriad songs in the 1960s, before and as he was starting his solo career.

When Campbell moved to Los Angeles in 1960, he got a job as a writer and demo singer / player for a publishing company; that led to work as a session musician. Campbell became part of the Wrecking Crew, an in-demand group of session players who worked on songs for everyone from Sonny & Cher to Frank Sinatra. They were producer Phil Spector's go-to house band, but were sometimes uncredited players; the late Leon Russell was also a member.
Flip through the photo gallery below to learn more about Campbell's work as a session musician -- specifically, about seven hit songs that, fans may not know, include his playing:

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