If Danny Fields didn’t exist, it’s doubtful anyone would dare invent him – unless that person was some future hipster Woody Allen setting out to make a wild new musical version of Zelig, about an unlikely figure who somehow happened to just be there for 90 per cent of the most interesting moments in American rock and roll across the dark, sweet, tumultuous decade 1965–1975.

Unlike a Zelig, though, Fields wasn’t just simply there, blending in. Variously journalist, record company scout, PR man, manager and general “underground mayor,” to quote Alice Cooper, he often helped shape the scenes around him, in ways we’re still benefitting from. He’s hardly a household name, but his ears are responsible for a lot of the music played in all the coolest households over the past forty years or so.

If you’re glad The Doors broke through, you should be thankful Fields, as their self-appointed publicist, was around to suggest to the record company that “the song about fire” should be a single. If you ever shook a hip to The Stooges or The MC5, you owe him a drink – he got Elektra to sign both bands unheard in a single phonecall to label boss, Jac Holzman; by that point, Holzman had made Fields his “company freak,” hired, essentially, to stay up later than everyone else.

Ramones fans should know him as the man who discovered the band at CBGBs in 1975 and became their first manager. They parted in the early 1980s, when they agreed (wrongly) that they might make some money with someone else, but not before Da Bruddas wrote one of their most glorious songs in his honour, the chiming Christmassy tic-toc “Danny Says.”

Devoted scholars of American music’s ripped and torn underbelly might recognise Fields’s name from the footnotes through his various associations with The Ramones, The Stooges, The MC5 and the fountainhead itself, The Velvet Underground. But seeing it all laid out in director Brendan Toller’s documentary portrait Danny Says – that this one guy had his antenna up in a way that put him right in the middle of it time and again – is still remarkable.

More startling yet, though, are the extra flashpoints the film uncovers. You know those giddy photographs of Bob Dylan meeting Patti Smith for the first time in Greenwich Village in 1975? Well, Fields was the guy behind the camera. Before that, he was the guy who first invited Smith and Robert Mapplethorpe, two wide-eyed kids persistently hanging around, to join the backroom gang at Max’s Kansas City. A few years before that, in the same legendary New York hangout, he introduced David Bowie to Iggy Pop.

If that’s not enough, how about this: in 1966, as a mischievous young editor on teen fan mag Datebook, he was the one who realised that a quote John Lennon had given months earlier without fuss to London’s Evening Standard was worth pulling out and highlighting. Thus the world got the “more popular than Jesus” furore that saw The Beatles’ US tour met with bonfires and KKK death threats, and fuelled the band’s decision to stop playing live. (Paul McCartney confirmed as much to Fields years later when the pair were socialising, the result of McCartney having married Fields’s long-term pal, Linda Eastman, who he’d known since she was a young Datebook photographer.)

This makes for such a wide, fantastic Pop surface you can forgive Toller’s film for not getting far beneath. We get a good taste of Fields’s persona – dry, catty, sharp, simultaneously unimpressed yet in love with it all – but not much idea of what might tick inside. In this respect, the opening is most poignant. Illustrated with glowing home movies, we catch a glimpse of a very straight early life as a Jewish boy growing up in stifling suburban Brooklyn, where Fields was born as Daniel Feinberg in 1939. Already, though, there are kinks: his doctor father left a bowl of amphetamines out on the sideboard, like sweets, and Danny and his mother would regularly help themselves. (“But so was everyone,” he says.)

Openly gay, Fields went to Harvard to study law, but was less interested in that than, as he puts it, “hanging out with a bunch of dissolute faggots.” He dropped out and gravitated to Greenwich Village and quickly fell in with Andy Warhol’s Factory crowd just as it all started exploding, forming particularly close friendships with Edi Sedgwick, Nico (he was later responsible for bringing her to Elektra for her and John Cale’s magisterial Marble Index) and Lou Reed.

Shortly before his death, Warhol himself told Fields he’d like to make a film about his life. Toller’s documentary is likely very different to anything Andy might have done, but he’s indebted to Warhol for the lessons he taught Fields, who developed the habit of documenting his own life meticulously, down to regularly tape recording conversations with friends.

Toller has interviewed Fields at length over several years – essentially, the film is just like sitting down and listening to him tell stories – and brings in new contributions from Iggy, Alice, Jac Holzman and many others. But the real gems here come drawn from Fields’s sprawling archive of photographs, tapes and memorabilia. It’s worth the price of admission alone to hear his recording of Lou Reed’s uncharacteristically enthusiastic reaction the night Fields first played him The Ramones: “That is, without doubt, THE most fantastic thing you’ve ever played me!”

It’s perhaps telling that the documentary ends with The Ramones adventure. There’s nothing here about what Fields has done since. You get the feeling that he has plenty of stories to tell about the past four decades. But, then again, maybe those stories just aren’t as good.