When Pink Floyd released their career retrospective Echoes in 2001, almost one fifth of the songs were written by Syd Barrett despite his having left the band more than three decades earlier.
Mental health problems were blamed on drug use
He was the band's co-founder and initially its undisputed leader and principal songwriter - he even came up with the name, reportedly inspired by US bluesmen Pink Anderson and Floyd Council.
But he departed the group while battling mental illness after just one album, The Piper At The Gates Of Dawn, which he had largely written.
When Pink Floyd achieved global stardom in 1973 with Dark Side Of The Moon, Barrett was living as a recluse - as he continued to do for the rest of his life.
He was long gone as Pink Floyd amassed more than 200 million album sales throughout their career.
And it is not known whether he was aware of the band's highly-trumpeted stage reunion, after more than 20 years, at last year's Live 8 concert in London.
But BBC Radio 2 DJ Bob Harris says: "I truly believe that the spirit of Syd Barrett has always lived in Pink Floyd and what they do."
Tim Willis, author of the Barrett biography Madcap, agrees.
In those first three years Pink Floyd were "crafted in [Barrett's] image", Willis has written, "and they never quite put him out of their minds."
Harris witnessed early performances by Pink Floyd in London in 1966, and believes that Barrett was the creative force as the band evolved its radical, psychedelic style with extended, improvised sets and highly visual lightshows.
"In many ways they have been true to the legacy ever since," says Harris.
The decades of music that followed, including commercial highpoint Dark Side Of The Moon, had their "foundation stones in the work that Syd Barrett did with Pink Floyd in '66 and '67", says Harris.
He adds: "A Pink Floyd album now sounds much more finished and smooth than it did then, but the creative forces that are informing it are much the same.
"It's just a sophisticated version of what they were doing then."
In a statement following the announcement of Barrett's death, Pink Floyd themselves acknowledge their former colleague was "the guiding light of the early band line-up and leaves a legacy which continues to inspire".
But perhaps 1975's Wish You Were Here album offers a more suitably cryptic and poetic tribute to Barrett.
"Remember when you were young, you shone like the sun. Shine on you crazy diamond.
Now there's a look in your eyes, like black holes in the sky. Shine on you crazy diamond."