Image copyright Carl Hyde Image caption Nuriddin performed the full album for the first time in London in 2014

Hustlers Convention, released in 1973, is regarded as one of rap music's great forgotten classics, influencing hip-hop artists from Chuck D, Ice T and the Beastie Boys right up to Nas and Lupe Fiasco.

But few people have heard it and most don't even know it exists. A new documentary is hoping to rectify that.

It was a full moon / In the middle of June / In the summer of fifty-nine / I was young and cool / And shot a bad game of pool / And hustled all the chumps I could find...

A tale in rhyme of two street hustlers named Sport and Spoon, a catalogue of criminality told in the first person to a funky soundtrack supplied by Kool and The Gang.

The Hustlers Convention by Lightnin' Rod was released to very little fanfare more than 40 years ago. Lightnin' Rod was a pseudonym of black activist and founding member of The Last Poets, Jalal Mansur Nuriddin.

"The idea was to consolidate all the hustles and put them in one place at one time but have a moral of the story at the end," explains the now 71-year-old Nuriddin.

The album took the form of a toast, a form of rhythmic spoken poetry traditionally performed by prison inmates. The urban first-person narratives often portrayed heroic events in the teller's life.

"Toasts were part of the African-American subculture," explains Nuriddin. "It's a descendant of the old tradition of storytelling.

"Toasting was like reminiscing on a highlight of a time in your life when you had everything you wanted but sooner or later you were going to lose it and that's the point I was making with the Hustlers Convention."

Image copyright Courtesy of Spectrum / Kaleidoscope Entertainment Image caption The documentary mixes historical footage and interviews with animated sequences

Image copyright Courtesy of Spectrum / Kaleidoscope Entertainment Image caption The album tells the fictional story of hustlers Sport and Spoon

Image copyright Courtesy of Spectrum / Kaleidoscope Entertainment Image caption The Hustlers Convention of the title was a fictional event inviting "dope pedlars, murderers and thieves, card shark gamblers with aces up their sleeves"

Image copyright Courtesy of Spectrum / Kaleidoscope Entertainment Image caption Nuriddin

But there was more to the tale of Sport and Spoon than just a record of their regrets and wrongdoings. Nuriddin also had a political point to make, which he illustrates by quoting his own lyrics: "The real hustlers who were ripping off billions from the unsuspecting millions who are programmed to think they could win.

"In other words, anything we do is penny ante compared with the CEOs and moguls and entrepreneurs, the tycoons around the world."

The album's release was marred by a legal battle over the instrumental score to Nuriddin's narrative. Kool and the Gang were signed to another label who threatened to sue United Artists and the album was withdrawn and licensed off.

Just 20,000 or so records had been sold.

Despite its controversial subject matter, coarse language and very little radio support, it spread through inner city US communities like wildfire, passed on largely through word of mouth.

Nuriddin's compelling, if perhaps fanciful theory is that, rather than a legitimate legal issue, it was willingly held back by a powerful record industry elite.

"That's why nobody knew about it, that's why it only sold on the underground because people in power didn't want none of that exposed," he claims.

"Even though it [dealt] with what we called the black hand side of things, the classic hustles such as 'dope pedlars, murderers and thieves, card shark gamblers with aces up their sleeves'. But it might have shed some light on professional hustlers who supply the lower echelon hustlers who deal on a street level.

"Particularly the line where I say, 'Crooked politicians spending campaign expenses', this occurs repeatedly, even before Hustlers Convention was written, politicians were getting paid off or looking after their own personal interests, so that had a lot to do with it.

Image caption The documentary has been produced by Chuck D

"And at a lower level, the street hustlers didn't want a light shone on their activities. But I really wrote it so the youth wouldn't want to emulate these hustlers and want to be like them."

Now, 42 years later, Nuriddin, who lives in modest accommodation in Atlanta, Georgia is yet to see much money from the album.

"Nothing to speak of," he says. "If I caught up with someone, they might give me what they got in their pocket, that's about it, nothing official. Unless I can get an accountant and auditor and a showbusiness lawyer on a Johnny Cochrane level.

"It was deep, I mean the hustling of the Hustlers Convention was a story in itself. I live hand to mouth man, I chose the message over the money so I can't be bought."

Filmmaker Mike Todd, whose previous work includes the Joe Frazier documentary When the Smoke Clears, uses a mixture of animation to tell the story of the album, and places it within a wider discussion on the American black art movement of the 20th Century.

Contributors include poet and writer Amiri Baraka and British poet Lemn Sissay alongside rappers Melle Mel, Ice T, Immortal Technique and KRS-One.

Image copyright Getty Images Image caption Melle Mel, also considered a pioneer of hip hop music is a huge fan of the album

The album has been sampled by artists like Wu-Tang Clan Jungle Brothers and Nas, who used it on Sekou Story from his Streets Disciple album.

The sound effects of rolling dice, jazz clubs, car chases and gunshots foreshadowed producers like Dr Dre and DJ Premier.

Stylistically, Hustlers Convention can still be heard in something like Lupe Fiasco's The Cool album, which also takes a loose narrative from the point of view of three characters, the Cool, the Game and The Streets.

All this has led to Nuriddin being referred to, somewhat grandiosely, as the Grandfather of Rap, it's not a title that he shies away from.

"Well I am a grandfather, its true but I don't beat my chest about it. I was rappin' when they was nappin'.

"I defined RAP as Revolutionary Arts Proverbalisation because those raps were street proverbs, there was a lot of street wisdom in there. In Hustlers Convention I talk about the 'masters of street-ology', how to stay alive on the street and make money at it which was very difficult."

But while the production of that early record was a template on which the modern form of rap music has been modelled, what about the lyrical content?

Hustler's Convention grew out of a time of great civil unrest, protest movements, assassinations of black leaders like Martin Luther King and Malcolm X, and the Vietnam war.

Nowadays with many rappers still boasting of their rags-to-riches tales with seemingly little regard for morality or social consciousness, Nuriddin insists that something indefinable has been lost.

"It's not evolving," he says. "You have to have correct knowledge to covert into wisdom so you can have something to say. I didn't start out as a rapper, rap is just an ingredient in poetry.

"The word rap means indictment, a rap sheet is how many convictions you have, if I rap on a door it's a sharp sound so the literal and figurative definitions of rap in American-English are there. In films with Humphrey Bogart and Jimmy Cagney, they talk about a bum rap, meaning charge.

"The thing has to be true to the meaning of the word, it can't just be nursery rhymes. The thing I can be happy about is giving youth a voice which they are still using today."

Hustlers Convention is in cinemas from 26 June.