When Peter Green presented “Oh Well” to his Fleetwood Mac bandmates at the end of the ‘60s, he couldn’t have predicted he was delivering an immortal work of rock and blues crossover. And even if he had known, he probably wouldn’t have been impressed.

Green already had a reputation as one of the leading British blues guitarists of the era, having replaced Eric Clapton in John Mayall’s Bluesbreakers before forming Fleetwood Mac in 1967.

A couple of year on, however, and his dabbling with drugs along with an insatiable creative drive meant he wasn’t happy with his lot. And while “Oh Well” became one of the blues-era Mac’s trademark songs, the late Green was always unhappy that most people only heard its first part, while he much preferred the classical guitar-powered second part.

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“You miss the best bit, the Spanish guitar break,” he told Mojo in 1996. “The first side was what we played on stage. I didn't think it would be a hit and I used to hate playing that one because we played the part that wasn't as good. I wanted a bit of moody guitar playing. They wanted the bit that was easy to do, that everyone knew.”

The two-part approach was entirely deliberate – he once explained that it “represents my two extremes… as wild as I can be [then] my first sort of semi-classical attempt.”

Hear Fleetwood Mac Perform ‘Oh Well’ (Part 1)

In 1994 Green told Guitar Player: “I had the idea after hearing some Spanish guitar music on the radio one day while I was riding in the back of a car. It was written and played on a Ramirez Spanish guitar I had just bought… What became ‘Part I’ was just intended as a throwaway riff for the B-side, but it became the A-side.”

Launched in 1969, the first part of “Oh Well” reached No. 2 in the U.K. and No. 55 in the States, making it Mac’s first American success. Accounts vary over whether Green or the record label pushed for its release, although it seems unlikely that the guitarist would have wanted it to happen. But it’s often said that bandmates Mick Fleetwood and John McVie (whose named Green chose over his own to title the group) wagered him £8 each – about a third of a week’s average wages at the time – that it would flop.

Hear Fleetwood Mac Perform ‘Oh Well’ (Part 2)

The call-and-response element is easily recognizable as an influence on Led Zeppelin’s “Black Dog,” but the impact of “Oh Well” goes much deeper. The long list of artists having covered the track over the years includes Slash, Aerosmith, Deep Purple, Billy Gibbons, Tom Petty and Ratt. Jimmy Page paid his dues when he performed it with the Black Crowes, as heard on 2000 album Live at the Greek.

How Peter Green’s Feelings on ‘Oh Well’ Echo With Slash

Green’s feelings about the song contributed to his sudden departure from Mac the following year; but that didn’t stop the band performing it through every decade of their existence – right up to their most recent incarnation, with Mike Campbell taking it as his only lead vocal at concerts.

The newest cover comes from Slash, whose relationship with one of his own songs carries echoes of Green’s feelings about “Oh Well.” Speaking of Guns N’ Roses classic “Sweet Child O’ Mine,” Slash told Music Radar: “It was an interesting pattern and it was really melodic, but I don’t think I would have presented it to the band…

“It was an uptempo ballad, which didn’t fit what Guns N’ Roses was all about as far as I was concerned. So that song annoyed me every time it came up in the set. It really bugged me!”

Hear Tom Petty and the Heartbreakers Perform 'Oh Well'

Watch Billy Gibbons and Steven Tyler Perform 'Oh Well'

Hear Jimmy Page and the Black Crowes Perform 'Oh Well'

Hear Slash and Chris Stapleton Perform 'Oh Well'

Hear Deep Purple Perform 'Oh Well'

Hear Joe Jackson Perform 'Oh Well'

Watch Haim Perform 'Oh Well'

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Gallery Credit: Dave Lifton