It is eight years since comedian Richard Pryor died, aged 65. A new documentary sheds light on his life, his bizarre childhood and the demons that tormented him and may also be responsible for his genius.
There are a handful of groundbreaking comedians who have changed the rules of the game.
Lenny Bruce, Tony Hancock, Monty Python, Andy Kaufman perhaps.
Richard Pryor was one of those comedy iconoclasts.
He was not the first black stand-up comic. Bill Cosby, Redd Foxx and Dick Gregory came before him.
But Pryor was a "game-changer" whose on-stage style would make him the most influential comedian of his generation, especially for black comics such as Eddie Murphy, Chris Rock and Dave Chappelle.
The Emmy Award-winning Marina Zenovich, who made the Storyville documentary Richard Pryor: Omit The Logic, tells the BBC: "He broke the barriers about talking about race and sex.
"When you hear him do those routines they are making it easier for people of different races to talk to each other and laugh with each other. It was groundbreaking."
Her film shows how Pryor started out in the 1960s and was all set for mainstream success until he realised one night on stage in Las Vegas that he was not being true to himself.
Pryor dropped out for a couple of years and when he returned he introduced a sharper, more foul-mouthed style that was more "street".
His delivery, littered with the n-word, hit a nerve with black audiences and with those who caught his act through his hugely popular live albums.
After Pryor's death in 2005, British comedian Lenny Henry told the BBC: "I started listening to him in 1977, when a guy in a record shop had this album called That Nigger's Crazy. He showed it to me and I was going to punch him, but he said: 'Listen to it, that guy's really funny.'
"Apart from the use of the word 'nigger', apart from the prodigious swearing, I thought, 'This guy's a genius.' He documented every pain, every abuse he'd ever suffered in his life, and he made it funny."
In 1979 Pryor visited Africa for the first time. When he returned to the US from Kenya, he vowed never to use the n-word again.
Zenovich says: "Imagine what that moment was like for him. No-one knew who he was. It was like going back to your land. He decided to stop using the n-word. He had this epiphany."
Among those interviewed for the film were actors and comedians Robin Williams, Whoopi Goldberg, Lily Tomlin and Mel Brooks as well as a number of the women in his life.
Williams recalls the thrill of seeing Pryor live on stage: "It was like saying you saw [saxophonist John] Coltrane."
But Zenovich says several key individuals refused to be interviewed - Murphy, Cosby and actress Pam Grier.
Grier was one of many women in Pryor's life. He was married seven times to a total of five women.
The film tells how he dated Grier - star of many blaxploitation films in the 1970s - for 18 months but ended up marrying another woman whom he had got pregnant.
The son of a prostitute and a pimp, Pryor grew up in a brothel in the town of Peoria, Illinois, and later made wisecracks on stage about his bizarre upbringing.
He would also joke about his sex life, his marriages, his relationship with cocaine and even about having a heart attack.
But the quips on the surface masked a sensitivity that led to him "self-medicating" with alcohol and drugs.
Actor Stan Shaw, who starred with him in Harlem Nights, says: "Success doesn't change you. It just magnifies who you are."
Pryor's friend and producer, David Banks, said the comedian had about 13 personalities and while you could deal with nine of them, the other four were a nightmare.
Jennifer Lee, who was wife number four and seven and became his widow, recalls the time he discovered freebasing cocaine.
She says: "After two weeks of watching him getting addicted to this stuff I moved out. It was clear the drug had moved in and it had become his lover and everything. I did not exist."
The drugs may have helped to obliterate memories of his childhood, during which he was also abused by a neighbour.
Michael Schultz, who directed Pryor in the film Which Way Is Up?, says: "His sensitivity made him so brilliant as a comedian but some things were so painful that he wanted to be somewhere else."
His grandmother Marie Carter was a brothel madam and a dominant matriarch whom he loved, feared and possibly loathed.
Zenovich, who has made award-winning documentaries about film-maker Roman Polanski and disgraced French tycoon Bernard Tapie, says: "If his grandmother was alive, I would have done that interview in a heartbeat. But we went to Peoria and it didn't work."
So none of the Peoria footage made it into the final edit.
Pryor's grandmother's death arguably tipped him over the edge.
In 1980 he almost died after apparently dousing himself in rum and setting himself on fire while freebasing cocaine.
Pryor's doctors thought he was unlikely to survive the severe burns he suffered, but within a year he was back on stage making self-deprecatory gags about the incident.
He would light a match, wave it in the air and joke: "What's that? Richard Pryor running down the street."
Pryor bounced back with such success that he was offered a $40m (£25m) deal to make seven films for Columbia Pictures.
But apart from the occasional gem, such as Stir Crazy with Gene Wilder, his movie career was not a great success.
Zenovich, who admits being a huge Richard Pryor fan, says the Storyville film came about after Pryor's widow Jennifer offered access to his archives.
She says: "I thought it might be an issue that I was not African-American, but it wasn't. They hired me more for my heart and soul than for the colour of my skin."
The first edit of the film focused heavily on the fire incident and Zenovich says the audience at test screenings did not like it.
She says: "They said it needed to be more funny, not so depressing. He was such an icon we needed to deliver what the people wanted and they wanted to laugh more."
The finished film is set to be nominated for awards and Zenovich says she has heard there are plans for a Hollywood biopic of Pryor's life, with Michael B Jordan - who played Wallace in The Wire and recently starred in Fruitvale Station - playing the comedian.
Asked why Murphy, Cosby and Wilder declined to be in the film, she says: "People are more interested in their own story and they don't necessarily want to talk about public figures unless it suits them.
"They don't have to do it and they don't know how it's going to be done."
Pryor was diagnosed with multiple sclerosis in 1986 and his health deteriorated severely during the 1990s.
One of the most touching moments of the film is when his former lawyer Skip Brittenham wells up with tears as he recalls Pryor's last years.
Zenovich says: "It was never my goal to get him to cry. Jennifer didn't think he would talk but he said yes. He loved Richard so much. When he started tearing up he said, 'I didn't know I had this in me.'"
For her documentary Zenovich dug out some footage of Pryor being asked how he wanted to be remembered after he died.
In a rare moment of straight-faced candour, he said: "I'd like the people to see my picture and laugh and have stories to tell, tell some lies on me... just to bring joy."